Google Voice is the hardest service for me to replace. I don't see any alternatives on this list. I appreciate that they let me seamlessly send and receive calls and texts from my Android phone or my desktop. I have a hard requirement that my phone should be optional for all parts of my communication workflow.
Google Voice also works if you have internet access, but not mobile network connectivity, and it works while overseas to provide a fully-functional US phone number (you do have to use a standard paid US mobile number to set it up, but do not need to retain it afterward).
If someone else registers Google voice with that number, you're going to have a hard time. It'll be removed from your account, and you can't use Google voice without a US phone number.