Lost: Missing Pieces was a series of 13 mobisodes/webisodes which were released weekly on Verizonmobile phones and six days later on ABC.com between November 6, 2007 and February 4, 2008. Running between 1:22–3:27 in length, each mobisode fills in a narrative gap somewhere in the timeline from the first three seasons.
Featuring new content that is incorporated into the existing storyline of Lost, the mobisodes are considered a canonical extension of the series. Some stock footage and a deleted scene were also used. In total, Lost: Missing Pieces provided over half an hour of entertainment. Lost: The Official Magazine has featured a "making of" article for each webisode.
In July 2008, Lost: Missing Pieces was removed from the menu on the Lost site on ABC.com. At the same time, it was made internationally available, as opposed to being available in America only. They were also reintroduced in September 2008 when the site was redesigned. This time in a new Flash player with some additional text commentary, full-screen option, and the webisodes in reversed order. The quality seems to have been improved as well. The mobisodes were included on the Lost: The Complete Fourth Season (DVD) and Blu-ray releases, in full quality, and ordered after the production codes.
Lost: Missing Pieces received an Emmy Award nomination in 2008 for "Outstanding Special Class - Short-format Live-action Entertainment Programs". The nomination listed executive producers Damon Lindelof, Carlton Cuse, and Barry Jossen.  Although not credited (see below) for any individual mobisode on ABC.com, Jossen (who is now executive vice president of Creative for ABC Studios) was ABC's head of production at the time. 
Promo from ABC's site.
Getting the mobisodes into production was a two-year process that underwent several delays involving contract negotiations with actors, writers, and directors.
The mobisode series was originally announced in November 2005 under the name Lost Video Diaries. ABC had intended for it to be a spin-off series produced separately from Touchstone Television, introducing new characters played by non-union actors, similar to the mobisode series 24: Conspiracy. However, believing that it should be made with the union talent from the television series, the cast and crew of Lost called upon the major entertainment guilds to negotiate contracts for the mobisodes. 
Unions and "new media"
The opening sequence of Lost: Missing Pieces.
With the distribution of the Lost storyline on the forefront of new technologies (e.g., ARGs, podcasts, online viewing, and iTunes downloads), the financial issues of mobile content distribution had been wholly unknown to entertainment industry unions. Brenda Ching of SAG's Hawaii branch first encountered these issues with regard to Lost and described them to the larger national unions. In April 2006, the three major guilds negotiated a first-of-its-kind agreement in the industry between Touchstone and Lost, allowing for actors, writers, and directors to work under guild auspices and be compensated for the mobisode series. 
Lost Video Diaries
At Comic-Con 2006, it was announced that the mobisodes would be appearing during the Season 3 winter break. A preview was shown to the more than 4000 Lost fans present. The premise was that Hurley would find a functional DHARMA video camera and use it to record events on the Island, and that the video tape would have a previously unseen DHARMA orientation film on it. Some people speculate that some of this footage was shot and kept in storage  however it was never released to the public. As Season 3 came around, some of the cast members' contracts still had not been secured for the mobisodes, and Touchstone was being dissuaded by other industry producers from going ahead with the deals. As a result, production was further delayed, and the 13 week break was instead filled with Lost Moments. SAG (pdf file)
In June 2007, after Season 3 had aired, it was reported that the mobisodes would appear in the fall of 2007, featuring the entire cast. Carlton Cuse said the mobisodes would "give the hardcore Lost viewer more information that they probably weren't going to get through the show itself."  On November 6, 2007, the second day of the WGA strike (where one of the primary issues was the same sort of residuals that Lost cast and crew were receiving for the mobisodes) "The Watch" appeared on Verizon phones, and the series was revealed to be titled Lost: Missing Pieces.
The mobisodes were highly anticipated by Lost fans. Some portions of the fan community were displeased with the initial mobisodes.  However, the later releases were received far better. 
The mobisodes were filmed off mobile phones, re-encoded, and spread around the Internet. An example of the resulting quality can be seen in the credits screen below. Some of the high-quality versions leaked on the same day that the Verizon versions were released.
Both the Verizon releases and the ABC web releases lack a list of full credits. The only credits that appear on screen are the writer, director and cast members. However, a title card near the end of the Verizon releases reads, "Please go to ABC.com for cast credits".
The ending sequence of Lost: Missing Pieces.
Credits screen from a filmed Verizon version.
The following credits are identical on all the releases:
Plot:Christian is talking with Jack about his wedding, which is later that day. Christian reveals that his father disapproved of him marrying Margo, and that was the reason he didn't wear the watch given to him by his father on his wedding day. However, he tells Jack that he is doing the right thing marrying Sarah and passes the watch to Jack, who immediately puts it on.
Plot:Hurley comes out of Rose's and Bernard's tent. Neil comes up, and ask what he is doing. He looks at the bottle of DHARMA Cabernet that Hurley has dropped, and then asks if Hurley is going to make a move on Libby. He asks because he has his eyes upon her himself. Hurley tells him that he just now has a date with Libby. Neil reluctantly relents and walks away.
Plot: Ben and Jack play chess. Ben asks Jack if he would consider staying on the Island. Jack asks Ben if he intends to keep his promise to let Jack leave. Ben says that its not all up to him in that the Island will not necessarily let Jack leave. He also tells Jack that if he does leave, there might be a time when he would want to come back. Jack tries an aggressive move in the game and Ben immediately counters with another move (Castling).
Plot: While Michael is tied up at the decoy village, Juliet informs him that he can have the boat he requested to take Walt away after freeing Ben. Juliet tells Michael that Walt is special and that she's glad he will get him away from the Island. After assuring him that Ben will comply with this deal, Juliet then reveals the deal she has made herself with him, concerning her sister. She reminds Michael of the list they gave him, and wishes him good luck.
Plot:Juliet comes to Jack and tells him that Sayid and the others have not trusted her since she arrived at the beach camp. She reveals that they are right; she is still working for Ben and she has been sent to the camp to do tests to find out which of the women are pregnant. Jack asks her why she is telling him this and she tells him how she saw Sun's baby the night before and that she is tired of living Ben's dream.
Plot:Ben arrives to an urgent situation at Room 23. Juliet is there and tells him that he (presumably Walt) has done something again and that everybody is too scared to go in there. Juliet suggests that they could bring him back to Michael, but Ben refuses, saying that Walt is special and that Jacob wanted him there. Juliet brings Ben outside to show what he has done: a group of dead birds lay on the stairwell.
Plot:Dr. Arzt tries to convince Jin and Sun not to move from the beach to the caves as Jack has proposed. When Hurley and Michael tell him they can't understand him, he also expresses his doubts in Jack's role as a leader to them. However he changes his mind and decides to move to the caves after all when the roaring of the monster interrupts their conversation.
Plot:Sun is watching Jin fish and then walks into the jungle. There she buries a California drivers license when Michael runs by looking for Vincent. Seeing the license he picks it up and Sun tries to explain that she was going to leave Jin. Michael comforts her telling her it will be okay. The two almost share a kiss but Vincent appears barking before anything can happen, prompting Sun to leave.
Plot:Dr. Arzt is catching a spider in the jungle when Michael comes up and asks about the weather conditions for launching the raft. Then Arzt admits he made up the story about the monsoon because he wanted them to get help with the raft as soon as possible. He then tells Michael he went to Sydney to meet a woman whom he had met on the internet, but that she disappeared during their first dinner in a restaurant.
Plot:Jack is searching for supplies when he meets Ethan Rom, who gives him a case full of medicine that he says he found in the jungle. Ethan mentions that Claire might have to deliver the baby on the island, and Jack thanks him for his assistance. Ethan tells Jack his own wife died in childbirth along with the baby, and they both hope that rescue is on the way.
Plot:Hurley, Michael, and Jin are playing golf on the golf course. After Jin misses a putt to win the game, he goes on a temper-tantrum, shouting in Korean. As Hurley and Michael look on, Jin lets out all of his anger: he is unhappy, he doesn't want to be pitied, nobody understands him, and he is tired of the handcuff on his wrist. As Michael and Hurley eventually leave, Jin sits down, half crying, and repeating "I'm so alone."
Plot:Amelia arrives early to Juliet's for the book club meeting. She notices that Juliet is upset about something, and asks if it is Ben. Juliet says that things have gotten awkward between them, but Amelia presses further, suspecting there is something more. Juliet then requests that Amelia not tell anyone what she is about to show her. As Juliet is about to reveal Ben's X-rays, they are interrupted by the doorbell; presumably other book club members have arrived.
Plot: Vincent is running through the jungle on the island, when he encounters Christian Shephard. Christian tells Vincent to find Jack and wake him up because he "has work to do." The first scene of "Pilot, Part 1" then replays with Vincent encountering Jack as he is regaining consciousness.