OK - going out on a limb here.
Don't know if this is related to you or not, but the last Evo update borked Sirius/XM radio, fix is here:
http://androidforums.com/evo-4g-sup...9470-sirius-xm-not-working-2.html#post2117028
You can do ##DATA# and View without an MSL to see what those are set to, on the Evo it was:
http pd proxy port = 8085
http pd proxy address = pd.vog.sprintpcs.com
Those settings worked fine for months, so they're not the problem per se, but rather some combination of things mucking it up - changing them on the Evo has fixed that problem without side effects.
You'll need to contact Sprint to get your MSL or do a temporary root and use MSL Reader (free in the Market). You'll have to talk to others already posting here about root, I've no firsthand info on doing it personally. (I'm a huge advocate of only recommending things I know.)
If you change those settings and it still doesn't work, change them back to original.