Major wireless carriers in the US have promised to unlock customers' phones or tablets once they've paid off their contracts, beginning today. This is the result of an agreement the carriers made with FCC Chairman Tom Wheeler in late 2013; the deadline to comply with all portions of the agreement arrived today.

The two key provisions are as follows:

Postpaid Unlocking Policy. Carriers, upon request, will unlock mobile wireless devices or provide the necessary information to unlock their devices for their customers and former customers in good standing and individual owners of eligible devices after the fulfillment of the applicable postpaid service contract, device financing plan, or payment of applicable early termination fee. Prepaid Unlocking Policy. Carriers, upon request, will unlock prepaid mobile wireless devices no later than one year after initial activation, consistent with reasonable time, payment or usage requirements.

Carriers must also post unlocking policies on their websites (here are links for AT&T, Verizon, Sprint, and T-Mobile), provide notice to customers when their devices are eligible for unlocking, respond to unlock requests within two business days, and unlock devices for deployed military personnel.

The requirements are part of the CTIA Wireless Association's Consumer Code followed by the four major nationwide carriers and others. Carriers were required to follow any three of the six requirements by May 11, 2014, and all of them by today.

Unlocking a phone allows it to be used on any compatible network, regardless of carrier.

Wheeler pressured carriers to unlock consumers' phones after a strange turn of events made it a violation of the Digital Millennium Copyright Act for consumers to unlock their own devices. Congress and President Obama took action last year to let customers unlock their own phones, but that didn't require carriers to do so on customers' behalf.

Actually getting a phone unlocked in practice can be a frustrating experience, as our own Lee Hutchinson can confirm. Let us know if your carrier gives you any trouble.