T-Mobile's got a new option for all you commitment-phobes out there. Pay By The Day will get you your very own cell phone for as little as a dollar a day, if you can live by the rules of cheap calling.  In TMo's own words: 

Pay By The Day gives customers the wireless value they want without long-term commitments. The new prepaid plan only costs $1 per day for the days the phone is used. In exchange, customers get free T-Mobile to T-Mobile calling all day and unlimited nationwide calling from 7 p.m. to 6:59 a.m. All other domestic calls are just 10¢ per minute and text messages are 10¢ to send and 5¢ to receive.
 
Pay By The Day joins a growing family of prepaid options from T-Mobile, including Pay As You Go (previously named T-Mobile To Go) and Sidekick Prepaid (previously named Sidekick To Go). More information on T-Mobile's prepaid plans can be found at: http://www.t-mobile.com/shop/plans.