Yes, that was similar to my experience with VZW and Lingo, which also had simul ring. I didn't use VZW voicemail but had my unanswered calls forward to my Lingo line, where they would go to Lingo voicemail if I didn't pick up. If I turned the cell phone off, the calls would not ring my Lingo phone but would go straight to voicemail. So I left my cell phone on (going out of range was not a problem, since by definition I wasn't at home to get the call on the Lingo phone).

I think the behavior on VOIPo is different. Try it.