Data speeds SLOW while on a call

Should the internet data speeds drastically drop on 3G as listed below? My internet seems to drop to a crawl when I'm on a phone call. I've done some speed tests comparing speeds to verify my experience. First I got on a call, ran a speed test with the speedtest.net app. Then I immediately hung it up and restarted the app and test. Each test was from the same server… the results are below:

On Call 1:

0.46 Mbps down / 0.01 Mbps up

Off Call 1:

2.79 Mbps down / 1.23 Mbps up

On Call 2:

0.48 Mbps down / 0.01 Mbps up

Off Call 2:

1.33 Mbps down / 1.17 Mbps up

Restarted Phone -

On Call 3:

0.54 Mbps down / 0.01 Mbps up

Off Call 3:

1.36 Mbps down / 1.17 Mbps up

Reset Network Settings -

On Call 4:

0.54 Mbps down / 0.01 Mbps up

Off Call 4:

1.42 Mbps down / 1.22 Mbps up

Any ideas how to fix this? Hardware issue? Software glitch? I just had my phone replaced 2-3 weeks ago because of a faulty home button and have been noticing this since then. I did a restore from my previous phone when I firs tgot it. As of this moment, I haven't done anything to try to resolve it, with the exception of restarting the phone and resetting the network settings. I have the latest iOS 4.3.3.

Thanks