Actually, a bit more complicated. I had to add Pebble Time Steel to the mapping in the source, recompile, fix few bugs, recompile some more... ;-)

But eventually - yeah... Pair, open pebble app, show phone info, notice firmware upgrade, press upgrade button, confirm, wait during upgrade, wait for watch reboot and bam! ;-)

At the time Jolla Phone was the only phone I had, so I didn't have a luxury of activating it using Pebble original software. But it wasn't that hard. Firmware upgrades was working in pebbled for some time. The issues were merely with integrating new hardware platform, into pebbled sources.