So I have to be honest, I was just as happy with my google voice account (maybe more so, but time will tell) when I could not use it on my iphone. Now you might be asking why, and maybe my use case is not common, but google voice fills a nice roll in my life.
1) Random people at bars get google voice #
2) Companies that require a phone number get google voice #
Pretty much my google voice number is like my spam e-mail account. If you got this number, well good luck getting a return call. The ability to make calls from this number is nice if I ever do return a phone call from some random girl at a bar or some company that really wants to talk to me about why I downloaded their white paper.
The only other use case that I can see myself taking advantage of is the free SMS, although to be honest, it's more of a pain to let all of my contacts know who is texting them than it is to pay the $5 a month for my SMS plan.