The only issue might be that you won't be notified of new voicemails on the P280 once T-Mobile rolls out its new voicemail system in your area.
Currently, we just get a text message saying "you have x new voicemail messages" when a VM arrives, but apparently T-Mo is slowly changing the system to use a true voicemail indicator rather than a text message.
This is just a guess on my part, but it could be the only potential problem with the P280 and voicemail.