Ok, what do you see above the arrows when you're connected? If it says EV, you're in EVDO coverage (i.e. - high speed). If you see 1X above the arrows, you're in National Access coverage. If you're in National Access coverage, when the arrows are solid, you can't receive a call.
I use an Exchange Server to synchronize my Microsoft Outlook with my Treo. This uses a good deal of network activity...which is why I set my Treo to sync every hour when I'm in National Access coverage.
AS = Active Sync
Hope this helps
