I ported my phone number to Palm Pre phone but the voicemail function did not changed it's number and so pressing the Voicemail icon or pressing and holding the number 1 always dialed the old number. I called Sprint, they walked me through reprogramming that particular function. It works now! If you need yours corrected, call them on another phone. They will have you punch in a reprogramming code (sorry, I forgot the reprogramming number) then once you key in the new phone number for dialing voicemail, save it, reboot it. That's it.
I hope this helps those with a similar problem.