I don't have this problem. If ur mom uses it, flash Hypersense Nova, bit more friendly towards the user.
Thanks, I installed hypersense nova, it's a great rom. However no effect on the one ring issue.
You don't have a wild card (*) set in the call settings/blacklist do you?
Well after hours of trying stuff I've isolated this to be an issue between Google voice and t-mobile prepaid service. I tried other roms, even other phones, put the Sim in my galaxy nexus and it did the same thing, one ring.
It happens even when a google voice caller calls even her actual T-Mobile phone number, as well as any calls coming in from Google voice on her phone.
So it's 100% not a ROM issue, not specific to the nexus one or even her specific phone.
I spent hours on the phone with f###ing t-mobile trying to get them to look into the issue, but the would not acknowledge this issue or even send it to engineering.
I gave up and stopped using her Google voice number, which is a pain, she was using that as her primary cell number.
Problem still is that i use Google voice to make all my calls so no matter what my calls only ring once on her nexus one.