Well, we had a feeling that the GSM/EDGE radio in the HTC Touch Diamond was secretly quad band rather than triband given HTC's history with the original Touch and the fact that triband GSM radios aren't so common these days. Oh, and there were phone band setting preferences that included mention of 850MHz.
For those who are wondering what this is all about, the 850MHz band is used by AT&T in the US. This means AT&T folks can use the Touch Diamond on AT&T (if you're willing and more importantly able to hack your device). This will get you GSM voice and EDGE, but the 3G radio's hardware does not support the US bands, so no love there.
The ever-ingenious and ambitious folks at XDA-Developers got it all working. There are a few threads to muddle through there if you want to flash your device's ROM and add 850MHz support. We did it to our Diamond with complete success and now we have 850MHz and have our Diamond working great with an AT&T SIM (we have only 850 on AT&T in our area). Thanks XDA Devs ROM teams!
Here's the short version of the story: 1) You'll need to upgrade the GSM radio firmware on the device with the version on XDA Devs. To do this you'll fist need what's called a Hard SPL. This unlocks your device to be flashed with unsigned ROMs. It will wipe out your device (hard reset) so back up first. It's OK to restore afterward. Visit this thread to find the OliNex hard SPL: http://forum.xda-developers.com/showthread.php?t=400950 . Read the thread and related materials on that forum to find out how to use it (it's not all that hard). You must use Windows XP or Vista to do the ROM flashing in these steps. You may need to register as a member of the xda-developers.com forums if you're not already a member, to gain access to some of the required files mentioned in this post.
4) Use RUU to flash your Touch Diamond with that radio version (un-rar the radio ROM first so you have an .nbh file in the same folder as DiamonCustomRUU.exe). This part will not hard reset your device .
Again, this is for your geeky types who are comfy with flashing ROMs and have an idea what I'm talking about. If you're a newbie, be very careful or your device might be stuck in bootloader mode. If you don't know what bootloader mode is, this process isn't for you .
850MHz reception is quite good, and we're thrilled at this solution until a true North American unlocked version of the Diamond hits the market. Remember, this will NOT get you 3G, just GSM and EDGE.
After doing all this, if you'd like to verify your phone is on 850MHz, use field test mode. You can enter field test mode by entering *#*#364#*#* using the keypad.
-------------------- Lisa Gade Editor in Chief, MobileTechReview