Anyone know the differences in performance between using a GPRS PCMCIA Card or GPRS via a Bluetooth Phone.. 

They both have the same bandwidth capabilities.  I would think the answer to your question lies with the carrier of the signal, though.  The PCMCIA card recieves the signal just like a cell phone and then has a direct connection to the computer.  With your bluetooth phone, the phone has to recieve the signal and then re-transmit that signal to the bluetooth antenna in your PC.

Given this, the PCMCIA would seem like it would have an advantage, since it is directly connected to the PC with little opportunity for interference.

PCMCIA cards generally have a higher GPRS class than phones PC cards are generally class 12, while most phones are 8 or less.

thanks