The Rock Band® for Android, iPhone, Palm and feature phones title is owned and operated entirely by EA. They have announced that as of May 28, 2012, online service for this title will no longer be available. The game will still be playable on your device but online play and services will be discontinued.
You can read EA's announcement at the following page:
This change will only affect Rock Band Mobile. Any questions regarding this change in service can be sent to EA at their portal: