T-Mobile is now offering $1 per day calling with free T-Mo to T-Mo calls and unlimited 7pm-6:59am calls. The details:

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). With no annual contract, no credit check, and no monthly bill, prepaid plans are a simple, direct way to go mobile.