Secret Keystrokes for your Cell Phone

There are keystrokes to check your cell phone usage. Dial the code then press CALL. The call is free.

Verizon
To Check Balance #225
To Check Minutes #646
To Check Data Use #3282

T-Mobile
To Check Balance #225#
To Check Minutes #646#
To Check Data Use #674#

AT&T
To Check Balance *225#
To Check Minutes *646#

Sprint/Nextel
Voice Menu for All *4

For Verizon, T-Mobile and AT&T, you call, and a report gets text messaged back to your phone. Mine looked like this:
MINs Remaining
As Of: 06/26
Anytime: 650
N&W: 5,000 (Nights & Weekends)
M2M: Unlimited (Mobile to Mobile)
RO: 4,995 (Rollover)
RO exp: 450 on 07/23/07 (Rollover Expiring)