Good 3rd party Google Voice apps for iOS?

If you're still watching this thread, I don't know if any of these apps support multiple Google Voice accounts. But the four Google Voice apps I came across while recently evaluating them are GV Connect, GV Mobile, Think Messenger, and Talkatone. Have you checked those four?

Also, there is some form Google has online for porting a Google Voice account from one account to another. I don't know what happens to the phone number on the account you're porting to. And, my experience is it's hard to find answers anywhere as to what happens during these more complicated procedures with Google.

And Google seems to have no public customer support. You could try one of the Google discussion Groups on the Google Groups web site and see if anyone responds to a query.

The last option I can think of is port the number from one of your accounts to a cheap prepaid mobile phone, then port from the mobile to your other Google Voice account. In this last Google account, when the ported number comes in. Your old number will expire in 90 days. But there will be a link next to your old number that says "Make Permanent". You can click that button for $20 and keep your old number (in addition to your ported in number) forever.

There will be charged for doing it that way. Off the top of my head, Google's total charges would be $42, and if you got the cheap prepaid phone from T-Mobile, they'd want like $10.

There's a good document written by Obihai that describes porting a number to a mobile phone so you can then port it to Google Voice. That document is written for people who want to get their home number to Google Voice, but it's basically the same process of getting from one Google Voice account to another Google Voice account.

I just thought of one last option. Get two different apps to access Google Voice. Use one app for one account and the other app to access the other Google Voice account.