I have an off-grid cabin with satellite internet and I wanted to set up a static node to act as a relay hub for SMS over internet. I decided to purchase a Lenovo E7 tablet but found that Google Play said the goTenna app was not compatible (it runs Android Oreo and has no cell phone number). I was able to download the goTenna app from this link http://downloadapk.net/down_goTenna.html and found that it works fine. To install you have to give permission on E7 to download apps through Chrome and you have to set the goTenna App to assign a random GID instead of using a phone number.
Interesting, but not sure you’ll be able to support a SMS relay unless you do have a cellphone # activated on the tablet. The SMS relay assumes that at least one device on the network has cell service in order to forward the message onto the internet.