Last week, we discovered that the Verizon version of the iPhone 5 comes with an unlocked SIM slot. Our very own Jeff confirmed the theory by using his VZW handset to connect to AT&T’s GSM network.

While this was obviously great news, we were worried that things wouldn’t stay this way because carriers don’t generally like unlocked phones. But according to a new report, Verizon may not have a choice…

The Associated Press has confirmed with Verizon that the iPhone 5 comes unlocked, and that it will not be relocking it. This marks the first time the carrier has sold a phone that works on competing cell networks.

Remember last year, the first batch of Sprint-flavored iPhone 4S models arrived unlocked, but the wireless provider later issued a software update that relocked them. So it’s nice to hear that won’t be happening.

But that may not have been Verizon’s decision. MacRumors points to a section of the FCC network access requirements that the carrier agreed to when it purchased the 700MHz spectrum that it’s using for LTE:

“(e) Handset locking prohibited. No licensee may disable features on handsets it provides to customers, to the extent such features are compliant with the licensee’s standards pursuant to paragraph (b) of this section, nor configure handsets it provides to prohibit use of such handsets on other providers’ networks.”

Sprint, for its part, will unlock your handset after 90 days. And AT&T, as far as we know, is still only unlocking iPhones that are off-contract — though it did recently start bending its own rule a bit.