This is how I look at it. Although I know others could explain things better then me.
Anyone can get an OBiTALK account and Softphone number. Used with the OBiAPP and a Softphone like x-lite or PhonerLite, etc. They can setup a Softphone to call you at either Your OBi Device number, or your OBiTALK (Softphone Number) using OBiAPP, if you have it setup on a Softphone on your computer.
Also, if that same person only has a OBiTALK softphone number, and has it setup with a working OBiAPP/Softphone, you can call them.
Not sure how this all works for them without a "Gateway Device". I could be all wrong here.
Anyway....As you read different posts, you will find that there seems to be some trouble getting the Softphones working with the OBiAPP.
However, If I'm not mistaken, the Softphone number is also used with OBion for use on Smartphones.
I'll let someone who knows more about all of this take it from here.