I tested 3-way calling this morning by placing a call from RingTo on my OBi 200 first to my moto x, hit flash got dialtone then called my iPhone. I was able to carry on a fascinating conversation with myself between the handset attached to my OBi and my two mobile devices simultaneously; so, for me, it works.
I've got nothing against GV but, for my needs, I like RingTo a lot. As the upstart, I find them very willing to listen to customer feedback regarding future service enhancements.
Cheers! Roland