here's some info on them, followd by a link that could explain them even more
Lost: Missing Pieces is a series of 13 mobisodes/webisodes, available for viewing first on Verizon mobile phones, and six days later on ABC.com. Featuring new content that is incorporated into the existing storyline of Lost, the mobisodes are considered a canonical extension of the series. Each mobisode fills in a narrative gap somewhere in the timeline from the first three seasons. The mobisodes are released weekly, leading up to the Season 4 premiere, and are between 1:22–3:27 minutes in length.
http://www.lostpedia.com/wiki/Mobisode