I just got my new Nexus 5 and Ting SIM card. The migration was confusing. I tried using the feature within MY DEVICES called "Move this number to another device" but this will NOT work.
I called support and found that I needed to ADD DEVICE and as I moved forward it did let me then choose to replace my old phone and use that number (meaning I did not add a new paid line).
Followed the instructions.
Manually rebooted and waited about four minutes and BINGO. It ported.