Depending on which channel is used incoming calls are match to a NSP user registry using the following parameters/ fields in the User Profile :
Telavox – The caller number is matched to either Phone or Mobile phone.
Skype for Business (Lync) - The Skype for business calls are matched to Lync Address
Note! The fields Phone and Mobile phone are by default found in the standard User profile form, but if you want to use Skype or/and Skype for business you need to manually add these fields to the User Profile form. This is done in the Entity editor form editor.