An expresscard solution is coming out next month, I can't remember who makes it, but if it is for ev-do (not edge) you'll be able to use this.
In the meantime if your phone supports it, I'd get a data cable and connect it directly via USB.
I have a verizon razr v3c, and I have ev-do plan, I just connect my razr via usb cable and use the ev-do that way.
Here is the card that should be coming out next month that DOES work for your macbook pro:
http://acill.blogspot.com/2006/04/apple-macbook-pro-expresscard-for.html