This SPL is optional and optimized for hero and rogers roms, if you flash the spl make sure you have a nandroid backup or rom to reflash because you will need to do so.
The latest Radio version is 188.8.131.52I with a Baseband Version of 62.50S.20.17H_184.108.40.206I
Download the radio to /sdcard/update and download the SPL here to /sdcard/spl-signed.zip
Shutdown your phone and press Home + Power while booting to get to the recovery console, then press ALT-S to flash, once its finished and done rebooting twice, go back into the recovery console.
Press ALT+X for terminal, press Enter, then type:
mv update.zip latestradio.zip
mv spl-signed.zip update.zip
recovery #Sends you back to the recovery screen
Press ALT+S to flash the new SPL after your successfully flashed the new Radio!