Here are some links to walk you through the process of setting up with T38Fax, in approximately the order you'll want to read them.
Pricing Model
Popular ATAs
Free Trial Signup - If you're planning on porting in, choose a temp number for your trunk. Implementation Guides - Some are also linked from the popular ATAs page.
Recommended Firewall Settings - Directly connected ATAs can usually skip this part.
Recommended Fax Machine Settings
Number Forwarding - Useful if you want to use your T38Fax trunk before your port is complete.
Number Porting - You must activate your trial account to port in a number.