It is now very easy to install eWeLink on an Android tablet without a telephone number. Just get the latest version (2.2.5.1, 2016-11-30) from Google's Play Store. While it is described as "designed for phones", it will download to a tablet and an activation code will be sent to an email address without ever providing a telephone number.

Unfortunately, I could not install this new version on an older tablet with Android 4.0.4. But I still had eWeLink.2.2.5.apk (see Installing eWeLink on an Android Tablet). Once I installed that version on the older tablet, it did upgrade to version 2.2.5.1 and it does work for the most part. The appearance of the Loop Timer makes it difficult to use, and I have not tested Scenes.

If you don't happen to have the version 2.2.5 application package (and you won't get the 2.2.5.1 version following my previous post since the Play Store has the latest version since the 8th of December), you can install the somewhat different E-WeLink-2.1.13.apk (available here: http://www.raspberrypiwiki.com/download/E-WeLink-2.1.13.apk). An email address, without phone number, will get you an activation code. The GUIi is slightly different, the app looks like it can handle different types of devices, and I could not get it to "update" to version 2.2.5.1. Still, it if you are impatient to test your Sonoff, and you can't borrow or beg an Android phone and your tablet is too old to obtain version 2.2.5.1, then it is worth a try.

When I tested E-WeLink version 2.1.13, I created a new account (different email, new password). I tried to attach a Sonoff that I had in my original account. The application refused, saying the device belonged to someone else. I found that comforting.