If your going to use your cell phone, Verizon has the best system for accessing the internet. All you need is the software and a cable to connect to your laptop. Any Verizon store can help you out there. Their transfer rate is about the best you'll find. SprintPCS works the same way, but at a slower transfer rate. I believe Nextel also has the same type of access.
If you want to go third party, the best software to use is made by FutureDial.
http://www.futuredial.com You can purchase the software and cable for your phone on their website, or at some Radio Shack stores. It best to check out their website to make sure your phone is capable of being hooked to you laptop, and able to access the internet. You should be able to get connected for $50.00 or less, and as long as you keep it somewhat short, you shouldn't run up any additional charges on your cell phone.