According to this, Guitar Hero: Aerosmith is to release this June in Europe. The American version of the game has been officially confirmed for a June 29 release.
In other Steve Tyler news, it appears there may be more bands than Aerosmith in the game. This ad says it includes Aerosmith and “all their favourite bands”. In addition, a USA Today article claims the game will feature “opening acts” and the Aerosmith fansite club also reckons Run DMC will be included, although that’s probably just for Walk This Way.