Wanted to share my story in case it helps anyone else who have locked themselves out of the their Teslas...
Over the weekend I went to mountains. While skiing I lost physical key card (Model 3) and also the only phone with which I can unlock my car. Call it being double unlucky.
First, to unlock my car I tried to login into Tesla app from my friend's phone. While I was able to login into my Tesla account, I was not able to see the car, because the car was parked outside reception. In the Tesla Mobile App I saw error message among the lines "could not establish connection to the car".
Then I called Tesla roadside assistance to see if they could somehow help me. They offered to unlock the car remotely after verifying my identity. However, they encountered the same problem - car was out of reception and they could not ping it. Besides that, they will be able to only unlock the car, not start it. Once this Plan B failed as well, Tesla representative offered to send specialist to come over physically and unlock the car. I told them to hold off because I still had Plan C in my mind...
I asked my friend, who had weak data connection in few nearby spots, to create a WiFi Access Point with exactly the same SSID and Password as my home network to which I had connected my car in the past. The idea was to "trick" the car to connect to the Internet through this Access Point by pretending to be my home WiFi router.
Guess what? The car connected to this Access Point and it immediately became "unlockable" through Tesla App installed on my friend's phone.
I was a little bit worried that my home Access Point might have left some "fingerprints" on the car (like MAC address) and the car would notice this discrepancy and refuse to connect to this WiFi hotspot. But it didn't! Which was exactly what I wanted.
The morale of the story is -
1. try to at least once connect your car to home WiFi network and memorize your SSID and Password, so that you can create WiFi hot spot with same credentials and bring your car back online in case you parked it out of reception.
2. if security is of any concern, then don't connect to random WiFi hostpots with common names like "Default", "FreeWiFi" because someone later may imitate them and trick your car to connect to him (i.e. become man-in-the-middle).
3. make sure your Tesla account password is strong enough and you have memorized it.