For services that have feature parity with GV, I'd recommend ring.to. Note that ring.to is run by bandwidth.com, the same CLEC that Google Voice uses for most (all?) of its numbers, so porting is easy:

https://ring.to/#newservice

For a more hands-on alternative, Anveo is a good choice (and they have SIP and SMS short code support):

https://www.anveo.com/

ring.to sign-up seems to assume porting an existing number. Is there a way to sign up for a new number?

>RingTo launched over two years ago with a simple mission: help more people keep the phone numbers they love. In the spirit of moving forward, several changes are coming down the pipeline we want to share with you.

>In early 2016, RingTo will transition to a paid service and will no longer offer free accounts to new or existing users. But don’t worry, we’re making it worth your while to stay with us!

I'd say they haven't quite finished the new signup yet.

I guess this is a good thing? If it's paid it might stick around for a while longer.

Edit: not sure I'd touch them - http://us6.campaign-archive1.com/?u=9094a6314c49a804bd522a79...

I use voip.ms. It has a good service. Some limited SIP knowledge help if you wish to make it work ok.