After 10 tries I got my HTC M8 to communicate with a brand new iPhone 6.
What I tried was turning off data services, bluetooth and making sure there was no SIM card on the old phone.
It worked, I selected what I wanted to transfer (messages and contacts), transfer started, but was interrupted after 5%:
"Start over: The transfer was interrupted. Do not switch to other apps or turn off this device until the transfer is complete."
I tap "OK"(only option) and both phones go back to the first screen.
HTC is prompting for a code, while iPhone is still "transferring".
This is terrible. I thought the PlayStore reviews were just bad blood, but they really aren't.