Q: No-contract phone for international?

I'm planning to buy an iPhone 6 and I definitely need it to be Verizon as has better reception as my house.  I'll be doing some international traveling and heard that "roaming" is prohibitively expensive, and that I should get an "unlocked" phone to (I think) insert a local SIM card or something?  But on the Apple site it says no-contract is T-Moble.

Sorry.. I don't really understand how all this works.  Any advice appreciated.