If phone number in address book contains space like 1 800 1234567, Zoiper Pro fails to dial.
Regular Zoiper (not Pro) and old Zoiper Lite dial such numbers without any problem. As result of this, impossible to use android phone address book.
The workaround is to replace all spaces by dash (-) but I have hundreds of contacts in the address book, so, it is impossible to do.
The problem exists at least with US numbers that starts with 1 (11 digits format) or starts with +1 like +1-800-1234567(international format).