The times I asked I got answers ranging from "The default is 1111" all the way to "It's already unlocked, but it can't be made to work because we use CDMA and the others use GSM and the phone itself isn't compatible..."
...
It all smacks of "Customer Control" tactics
It smacks more of "I know nothing about that phone". Almost all Verizon phones are CDMA-only. TMobile is GSM. A CDMA phone won't work on GSM. That's all true, and has been since we started using digital signaling in cellphones (before 2,000, IIRC).
This particular phone has both GSM and CDMA modules in it, so it'll work on either, but it's one of the VERY FEW phones that will - and sales people don't consider "Cellphone Engineering Monthly" light reading. They just assume that, as it's been up until about last year, if it works on Verizon or Sprint, it doesn't work on AT&T or TMobile. And until then they were right.
But as far as getting the unlock code for the GSM SIM? Maybe if you started with customer service and slowly (it could take hours) worked you way up to engineering. Or if you happen to be friends with Lowell McAdam (CEO of Verizon) - a post-it note from him saying "give me the gsm unlock code for imei xxxyyyzzz" would get the unlock code in a few minutes.
But short of that, I wouldn't hold YOUR breath, let along my own.
Social engineering could work, though. "I'm planning a business trip to Russia next month, and I'd like to put in a local SIM when I'm there, so people could call me on a local number - and I'd need the SIM unlock code to do that," It's a business trip, Verizon will get you back when you return.
Oops, the trip got canceled. How sad.
You're not doing anything illegal - it's your phone, so you should have the right to put any SIM in it you want. (If it's part of a Verizon package - you got the phone at a subsidized price on a contract - be prepared to pay the remaining amount owed on the phone. And they could say that only the last 5 months of payment pay for the phone, so you owe the entire retail price. Nothing you can do about that. Unless TMobile has that "we pay your ETF" deal and you give Verizon back the phone and buy one from TMobile. All still legal. Just knowing that some of the rules of the game aren't printed on the instruction sheet.)