Reliable T1 Internet Provider in Phoenix, AZ

Hello,

I'm looking for a reliable T1 Internet provider in Phoenix.
Our current provider is Call One/Covad. We have so many
down times. We use this T1 for our LAN-TO-LAN VPN
connection to HQ in the Midwest. Two mornings in a row
I got a call from my contact in our Phoenix warehouse that
the "System is down!". I initiated a continuous ping to the
Phoenix router. It was not responding. So I placed a
call to the Call One tech support. The tech support rep
called and left a voicemail that the circuit is up, after 30
minutes. So I logged into the router and looked at the
WAN log. Another note, the T1 carrier has a netopia
router for this circuit and it uses ppp for authentication.

Thanks in advance for any suggestion.