From The XDAndroid Project

How to configure MMS

Go to APN Settings (Settings -> Wireless & Networks -> APNs)

Hit the menu button (different for every device, RHOD is the "Win" key) and add an APN

Carrier-specific Settings

Carrier MCC MNC MMSC Port User Pass
Sprint 310 00 80
Alltel 310 995 8080 Digit Phone Number) alltel

Menu -> Save APN.