Rock Band mobile costs $4 for a monthly subscription and $10 for a "one-time use on more than 30 handsets." We were a bit confused about that line, so we contacted Verizon, and the provider confirmed that a $10 payment unlocks the game for "unlimited use." So there you have it!
*Verizon has acquired AOL, Engadget's parent company. However, Engadget maintains full editorial control, and Verizon will have to pry it from our cold, dead hands.