if you are being charged for tmobile voicemails you need to update the voicemail retrieval phone number. just dial 222 and listen to prompts. when finished restart phone and you voicemails will be free .
I HAVE DONE IT AND GOT TEXT MESSAGE FROM T MOBILE ON BOTH BLACKBERRY AND IPHONE 4 CHANGING NUMBER AND NOW NOT BEING CHARGED FOR VOICE MAIL RETRIEVAL
extract from t mobile faqs ......
Why have I been charged for calling voicemail?
If you have stored your actual mobile number for voicemail you will be charged. You need a special voicemail number stored that can be set up by calling 222 from your phone. Simply follow the prompts and this will ensure you're not charged any more.