All right, already... this is untested, mind you, as I can't flash my own custom ROM at the moment...
Looking at the file PhoneApp_enUS.oprc from the 1.23 (and presumably other) versions of the firmware: The MBAR resources (1101, 1501, 1801, 1804, 7001) are identical to the MBAR resources (1100, 1500, 1800, 1803, 7000) in every way, except they lack the "Select Network..." option.
I have found the place in the code (see my previous postings in this thread) where it disables the "Select Network..." option by displaying a xx01 MBAR instead of the corresponding xx00 MBAR. Rather than patching the code, I think it would be safer and easier to simply delete the MBAR resources which lack the SN... option and replace them with the ones that have it.
This should be easy to do using PrcEdit2 (available at
http://shadowmite.com/tools.html):
1. Extract the file PhoneApp_enUS.oprc (or the corresponding language file of your choice) from your favorite custom ROM firmware.
2. Open PhoneApp_enUS.oprc using PrcEdit2.
3. Cut MBAR resources 1101, 1501, 1801, 1804 and 7001.
4. Copy and paste MBAR resources 1100, 1500, 1800, 1803 and 7000.
5. Renumber these new copies as 1101, 1501, 1801, 1804 and 7001.
6. Save PhoneApp_enUS.oprc and exit.
Then you would need to create and flash a custom ROM to test it out. If you don't know what I'm talking about, then you shouldn't be reading or attempting anything in this thread
Disclaimer: Anyone who tries this procedure does so at their own risk. I am not responsible for any adverse effects suffered by you or your Treo, including damage to life, limb or property.