Okiedoke...so unlock went well (after a few days delay) and my ole TMO SIM with Wally's $30/5GB plan is installed. Alas, for some reason wifi calling is not turning on, failing with an error 'reg99-unable to connect'. I had read on the TMO support site that this is often a result of 911 address not being on the account (mine wasn't) so I added it last night..and it shows up fine. After adding it, I had a notice that it might take an hour for it to 'propagate' to the server. Today, still same error. Do I need to do a custom APN to get wifi calling bak up and running, like it was on the MPCS SIM? Cheers!