Before I buy... is PinePhone actually open source?

[mypine]

I don't know of any carriers that actually check the IMEI anyway. if you call into customer service to swap phones they'll ask you for it, but the only number that matters is your SIM number. the IMEI is irrelevant and you can just swap phones indefinitely with no effect whatsoever

In Australia you can black list an IMEI with all 3 carriers from working if your phone is stolen, in the US Verizon restricts sim activation with a white list, any not on the list don't work.

More can be found in this thread

this is true, you can blacklist the IMEI, and if added to the blacklist it will be refused service, but you would need to blacklist it.

apparently some companies will blacklist for non-payment, but idk I've no firsthand knowledge of it.

at any rate, if you're not blacklisted, the IMEI is irrelevant still. you don't have to call in a new IMEI, nor will your account info register any IMEI change unless you explicitly contact your carrier to do so.

Where Verizon's concerned, there's not a blacklist, but a whitelist. Meaning if your phone's not on it, it doesn't connect to the network.
In my experience, I took a sim from a working phone on the verizon network, put it in the pinephone, made one successful call, and then every call I tried to make after that I got a network message telling me the phone I was using wasn't the one used to activate the SIM, and to replace the SIM in the original phone to get service.