HTC SDA (USA) / SP5m (Tornado)

I'm thinking of making the switch from Verizon to T-Mobile to be able to get this phone and better plan rates. I live in San Jose and occasionally need to drive to more remote No. CA locations for work. Any folks here with experience driving in Northern CA with this phone? How is coverage? I don't want to get stranded in a remote location with no phone service...

Thanks,

Maureen