I recently ported our family's cell phones from Sprint to Ting and this move has been working well. In conjunction with this move, I also ported my business line over to Google Voice and forwarded it to my personal Ting cell# as well as an Obihai VOIP ATA which replaced our household landline which was tied to voice service from Comcast Xfinity. The household land line was ported to RingTo which had offered free VOIP service to Obihai devices. While Google Voice worked great with the Obihai using XMPP protocol, the RingTo service used SIP protocol and I could never get it to work reliably.
In December 2015 RingTo announced they were discontinuing support for Obihai VOIP devices, and I am planning on porting the houshold land line over to Google Voice as well since GV seems to work so well with both Ting and the Obihai. The official porting instructions from Obihai suggest using a T-Mobile SIM card and prepaid phone as a stepping stone in the GV port, but I am planning on using an inactive Ting device for this purpose.
As far as I can tell, the only cost involved is the $6 activation fee for the inactive Ting device. I would be interested in hearing from other Ting subscribers that have or are contemplating integration of Ting, Google Voice, and Obihai. I'll let the forum know how this goes. Thanks.