Okay. I just got it working!
(I think a large part of the problem I was having last night was due to pbxes.org website issues, ie my account not deleting properly. [facepalm] )
I just now logged into pbxes, deleted the trunk, then deleted my account from the pbxes website. I then used the SIPDroid app on the phone to create a new account--and I put my Google Voice password in the 'password' and 'confirm password' fields. That set up a new pbxes account with the Google Voice password as both the ACCOUNT password AND trunk password.
If I understand you correctly, I can change the pbxes account password to something different--but the trunk password always needs to be the same as my Google Voice account.
ps. (I confirmed that the two test calls I made last night via Google Voice DID use some cell minutes. I wasn't clear on the use of the two different dialers: Voice vs SIPDroid.)
Now that it's working, how concerned to I need to be about whether or not Virgin Mobile (Sprint) 'allows' or 'doesn't allow' VOIP? In other words, if it's 'not allowed', what are the odds that I could get the stink-eye (or worse) from my cell provider?
Now that I've figured out how to MAKE calls, I'll have to tackle RECEIVING calls... :\