Try this...
I believe your issue is with the eHRPD 3G connection. I had problems when I first got the phone.
dial ##778#
select 'edit mode'
password 000000
scroll down to 'modem settings'
select 'Rev. A' and change it from 'eHRPD' to 'Enable'
That will put it on the normal 3G service.
The...