buy an app - message: "none of the accounts on your phone are supported" I tried to buy my first app on the HTC EVO.  My mail is working fine. 
It says "none of the accounts on your phone are supported",
then it offers me to 'add a google account". 
I click "Already have a google account/signin", then it tells me
"There is already a "xxx.xxx.com" account on this phone. 

My account is a Google App account, is that the problem? 
What is the get around, to create yet another Google Account juts for shopping?
This is a known issue with the Market / Apps accounts.  I believe Google has upgraded some Apps accounts to allow Market purchases, but if yours hasn't been upgraded then I believe you're out of luck and should create a regular Google account to use with the Market.