Does your V3c have the Verizon UI installed on it? If not, you should be able to connect using MPt with no problem. the Alltel firmware is not as crippled as the Verizon versions. Follow these steps to try and connect your phone to MPT:
You need to first make sure you are updated as far as you can go (currently 4.21a). Then click on "Menu", go to "General Setup" and click the "Communications" tab. Click "Change Modem" and follow the instructions. When you get to the "detect driver" screen, put a check mark in the box next to "Do not automatically detect driver. Select from list." and click "Next".
Choose "Motorola
CDMA" and scroll the list until you see "V3cm". Select this phone and click "Next". Then, simply click "Finish" and it will reload MPT. Your phone will be recognized and you will have access to the "Multimedia Studio" options.
If this does not work, then you may want to uninstall and reinstall the software. Then try the above procedure again.