Not only is the T-Mobile iPhone 6 Plus unlocked, but it works on Verizon!

[HotIce]

I wonder if using the T-Mobile version on other carriers will 'lock' the phone like the iPad does for AT&T.

 

[Shadowbech]

I wonder if using the T-Mobile version on other carriers will 'lock' the phone like the iPad does for AT&T.

No it won't, once the phone is unlocked, it will be permanently unlocked.

Only reason why the ipad does that is because of the Apple sim and keep in mind that it doesn't lock your ipad either. It just locks that sim to AT&T, but you can always take out and insert a verizon and it will still work.