Just found Htc Rezound is running on gsm and thinking of our spectrum on the same way. Both the phones have same specification with same chipset inbuilt, so there is a chance to test gsm on spectrum. Will you try and tell us?
[WIP][HELP NEEDED] Enable North American UMTS/HSPA bands (3G data on AT&T)
1) Download and install HTC Sync, HTC Diag drivers and DFS CDMA Tool (free version). Connect phone to PC and switch it to the DM mode (dial ##3424).
For detailed instructions look here, here or here
If ##3424# code doesn't work, download this app, launch it and select DMCmdBroadcastReceiver
2) Connect DFS to the first HTC Diagnostic Interface port (not 9K)
3) At the Equipment page check if Extended Build ID / MSM rev is MSM8660. If it's different, you've selected a wrong port.
4) Click Send SPC button to send SPC 000000.
5) Go to NV page. Set Start to 1877, End to 1878. Click Read Range. ITEM_1877 should appear in the list.
6) Select ITEM_1877. Values in the Edit NV box should be 87 03 68 00 00 00 02 00 followed by zeros.
7) Change the values to 87 03 E8 04 00 00 02 00. Click Apply changes and Write selected item. Click Read Range again and re-select ITEM_1877 to make sure the value as changed. Retry if not.
8) Disconnect USB cable and restart the phone.
9) Switch mode to UMTS Only and see if you get the signal.
TL;DR: Write 87 03 E8 04 00 00 02 00 into NV Item 1877 (NV_RF_BC_CONFIG_I) using the primary diag port.
Inspired by the Bionic on tmobile thread.
Here is a screenshot of my phone on HSPA network with a Red Pocket (AT&T MVNO) SIM card:
The only problem I noticed is that HSPA signal in my area is much weaker than GSM that comes from the same tower. But maybe this is how AT&T network works here. I don't have any other phone to compare.
Tested on the original 4.03.605.1 ROM (s-on, rooted).
May also work for other HTC "global" phones (Incredible 2?).
I also tried to enable 1700 MHz UMTS band for T-Mobile by writing 87 03 E8 07 00 00 02, but it has no effect. Probably, the hardware does not support it.
The weak signal problem is due to missing RF calibration for UMTS in 800 and 1900 bands. Loading a RF NV dump from a MSM8x60-based fully-calibrated phone might help. If you have a recent HTC GSM/UMTS phone and want to help, see this post.