The CTIA "volunterily" unlocking policy came to effect on on Feb 11, 2015 Consumer Code for Wireless Service In case if your provider refuses unlock or doesn't do it (for example Virgin Mobil reps instructed to give MSL code, which only unlocks it to another CDMA carrier), file complain with FCC at FCC Complaints
From my experience, AT&T has always unlock my phones for the past 7 years with no questions asked. In 2013, they unlocked a new phone 10 minutes after I renew my contract.
Yes some carriers are nice but others are not. If you ran into issues carrier unlocking and don't wanna jailbreak, complain to FCC.
Almost years ago, I unlocked my Galaxy S4 using hidden menu from this thread How to SIM unlock Samsung Galaxy S4 SGH-M919… | T-Mobile Samsung Galaxy S 4 | XDA Forums
I always buy unlocked phones. I travel a lot, and it's a lot cheaper to replace my Australian SIM with a local one in the country I'm in. I have permanent Australian and Chinese SIMs, and I buy a local SIM at the airport (or get a friend or relative to buy me one when I arrive so I know the number in advance) when I go anywhere else, if I'm going to be in the country for more than a day or two. It also means I don't get locked in to contracts. I'm on a pay-as-you-go SIM in Australia, in part because it's much, much cheaper, and in part because, in my job, I know how easy it is to get hold of people's call records if they're on post-paid contracts. And these days, unless you absolutely must have an iPhone, buying an unlocked, non-contract phone isn't expensive anyway. My current one cost about $150.
