This is the link to the mr2 radio for using Gingerbread roms:
[RADIO] The Obligatory Thunderbolt Radio Thread - xda-developers
Its the last set of links (both are the same) in the first post: Alpha Gingerbread radio
-Download the radio.
-Rename the zip file to "PG05IMG" (pg zero five img) if its not already named that.
-Do not unzip the file, leave it as it is.
-Place it on the root of your SD Card (do not place it in any sub-folders).
-Reboot your phone into bootloader... power off the phone.. turn the phone back on by holding down the power button and the volume down button at the same time until the phone starts in bootloader.
-You will be asked to install the zip file.. say yes with the volume up button. The zip will unload and when its done you will be asked to reboot the phone.. yes.
-You can check the installation by going to menu.. settings.. about phone.. software information.. baseband version. It should say 1.39.00.0508w, 0.01.69.0510w_3
After the installation, take the pg05img.zip off of the root of the sd card. It will cause problems for you if you ever need to go back into recovery through bootloader.