FWIW, I tried phoning ET to do seat selection (UA award bookings made in April 2017) using Skype from Oz. The USA, UK and Ethiopian phone numbers shown on the ET web site failed to connect. But the South African ET number (+27 xxxxx) worked perfectly. The process was fast and professional. All that ET wanted was the PNR and requested seats. The operator waited a few seconds and replied when she had a confirmation.