To check your T-Mobile voice mail from a landline (without consuming your airtime minutes) follow these steps:
Step 1. Dial 1-805-MESSAGE (1-805-637-7243) from any landline.
Step 2. Press * (Star) key
Step 3. Enter your 10-digit T-Mobile phone number
Step 4. When prompted, enter your password.
For a visual representation of T-Mobile VoiceMail shortcuts please refer to the following PDF diagram.
This tip works with both postpaid and prepaid accounts.