[la66209]

Ants' reply is on the right track.

The Sanyo MM-8300 has a tri-band radio which includes an AMPS mode and two CDMA bands, whereas the Touch only has the two CDMA bands. It is very likely that your good service in a rural area is a result of the AMPS connection. You may be able to confirm that by entering the Sanyo's field test mode (##33284# or ##debug#).

There's no practical way to get the Touch to handle AMPS signaling (although if you're determined, you might consider writing a software defined radio or grafting an AMPS chip into the device and then rewriting the supporting device software to recognize it) and hacking the PRL (generally distributed in binary) is time consuming and unlikely to reward you with the signal you desire. For several hundred hours of work, you might have something that would work specifically on these now aging handsets.

For a long term general solution that will work with your Touch or any other CDMA handset, I'd consider getting a Sprint Airave femtocell, a device about the size of a wi-fi router that essentially gives you your own Sprint cell tower. They're inexpensive (about $100) and from my experience they work very well. So well, in fact, that you may want to give up your land line if you haven't done so already.