IMO, Google Voice is high quality and quite reliable. However, there are a number of disadvantages. They do not offer 911 service, so those without landlines will generally add another provider such as CC. The OBi can be set up to route certain numbers, e.g. 911, 411, specific countries, etc., to CC and all other calls to GV. GV has essentially no support. Though serious problems are rare, should you have one, you could be down for a long time. If you want two concurrent calls, so you can make or receive a call while your wife is on the line, a fairly complex setup (including additional hardware) is needed.
As with any provider, GV has some restrictions over which you have no control. For example, voicemail will pick up after 25 seconds, no matter what. If you want the OBi to ring your cell phone, when the home phone is not answered in 15 seconds, you will probably be unable to answer the cell in time.
If you do a lot of international calling, you will find better rates with providers other than GV.
With a standalone setup, the phone connected to the OBi can make and receive GV calls. If you buy an incoming number from Callcentric, or use a free such as IPKall, you can also make and receive CC calls. The OBi LINE port can also be connected to the landline (even though other home phones are still connected), so the phone attached to the OBi can make and receive landline calls, too.
Of course, to test incoming calls on a particular provider, your contacts will have to call the corresponding number. If you decide to give up on the landline, you can port the landline number to another provider. With most, it's straightforward, but GV requires you to port it to a mobile first. You can use a cheap prepaid for this purpose.
You can set up the OBi to route 411 to some other number, e.g. 1-800-BING-411, which is a free automated system that (among other things) provides business listings. Providers that offer "real" (live operator) 411 charge on a per-call basis.
There are numerous companies that offer VoIP service, typically supplying pre-configured hardware. Of course, they vary in quality, reliability, features, support and cost. You might want to look at VOIPo, Phonepower, or Ooma. At the low end there's magicJack PLUS and netTALK.
