The easiest way to upgrade all radios, and PRI too, is to reun the Sprint Lover's All-In-One. Super easy from the SD Card. Then just flash any ROM you want, but the latest radios and PRI will stick. You will find it in the first post here:
[ROM] 12/05/10 | SPRINT LOVERS | 2.2 | 3.30.651.3 | Radio/Wimax/PRI All-In-One - xda-developers
It's so easy a Democrat can do it.