The agency, which won the business after a competitive pitch process, has been tasked with developing customer relationship management and mobile activity.
MIG's appointment marks the first time that Shelter has adopted mobile as a communications channel, a move it hopes will enable it to engage better with its younger supporters and consequently increase revenues.
The agency has created a channel that will enable Shelter to thank its donors for their monthly contributions via SMS. The messages will contain a URL that will take recipients to a dedicated mobile internet website, called Shelter extra, that has been created by MIG.
The site will carry regularly updated content including downloads, celebrity supporter updates, competitions and information about how to get involved in Shelter events.
David Jackson, Shelter's direct marketing manager, said: "By engaging users with the content and important work that Shelter does in the UK, donors will be reminded that their direct debit payments are more than just a note on a bank account statement, and that they are contributing to the fight against homelessness and poor housing around the UK."