I'm having a problem with my UMA connection where the connection would drop part-way into my calls. It would randomly happen a few minutes into the call, sometimes it doesn't drop, but usually it does. It has NEVER dropped when I'm not making any calls or when I'm just text messaging.
What can I do to keep the connection from dropping when I make calls?

What phone model are you using?
What OS?
What brand and model of router?
Also have you tried a connection at a friend's house or an available wifi such as at a cafe?

This was a problem with the 4.2 OS and with certain router models. Also there should be settings in the router that will help the connection. Could be either the router phone, both, router settings, or maybe just a poor quality internet connection.

I have a 8320
OS is v4.5.0.124
Router? I'm not sure, it's Chinese.... Internet works fine on it though.
Haven't tried it anywhere else yet except here.

Hmmm maybe I'll just wait til I get home to try out

Very likely the router is causing the problem. If you can get into the settings, and there's a way to turn QOS (Quality of Service) on or some other setting that prioritizes data packets it should help the problem.

Oh I forgot. Way back using WEP security worked way better than WPA. If changing that is a possibility, that also might help.

I've never been able to maintain a data connection while making a call, 8100, 8800 and 8900. AFAIK that's just the way it is, you can use data or the radio but not both.