I’ve had the worst problem with my T-Mobile MDA dropping calls about 4 minutes into a call. While the exact time of the drop varied (sometimes up to 10 minutes into a call) it was consistent to the point that everyone I talked to knew about when it would happen.

I’ve been searching all over the ‘net trying to find the cause of the issue and a fix/workaround for it. I finally found it! Not only are MDA’s having the problem, but many HTC Wizard class devices like the Cingular 8125.

The problem seems to appear after upgrading to the latest firmware from the provider – in my case the v2.26 ROM from T-Mobile (though I did see it as well with the 2.24 ROM for QTek on my device). The issue is that HTC had implemented a “feature” in the latest ROM that would help a data connection re-establish itself when it was unsure if the GPRS/EDGE connection was there. It would simply reboot the radio portion of the phone – whether a voice (GSM) session was in process or not!

The fix is to simply add a registry key that disables this new “feature”. Now that I know what the fix is, I needed to share it with anyone who passes by my blog. If you have this problem and use a HTC Wizard class device listed below, please check out the fix and the link to where I found it.

list

Here is the fix to the problem, and this page at XDA Developers clued me in.

Due to network conditions, signal coverage and some other factors, there is a small chance the data connection can become detached from the network, but the device is not aware of the detachment. This is normal in real world scenarios. Since data packages can be sent without any error being returned, the device may incorrectly think the connection is still valid. To correct this, HTC introduced a mechanism to watch for such conditions. After the device sends out data without receiving any network acknowledgment for a certain period of time, the device will try to detach from the network and re-establish the data connection. Usually this will silently re-establish the data connection without the user noticing it. Due to radio platform limitations, this task cannot be performed during a voice call. When both of these conditions are met (data being sent out for a period of time with no network acknowledgment, and an active voice call), the device will reset the radio to address the problem.

HTC has provided the following registry key setting to disable the auto-correction mechanism:

[HKEY_LOCAL_MACHINEDriversBuiltInRIL]

“GPRSStallWorkaround”=dword:0

I truly hope that this helps you with your HTC Wizard class device – I know I’m much happier now that I’ve found the fix for the problem.