According to a leaked internal Sprint memo, all Sprint iPhone 4S handsets sold starting today will have their SIM card slots locked to Sprint. It has never been fully clear how Sprint was shipping its iPhone 4S models but it now looks like they were originally shipping them with unlocked SIMS.

According to the memo, the SIM locking will be done during the iPhone’s activation process and it will be done invisibly. The customer will not see any notification of it happening.

What does this mean for any new Sprint iPhone 4S users? Well you will lose the ability to use a local SIM card if you travel out of the U.S. You will now have to have a roaming agreement in place with Sprint and pay the much higher call and data charges. One bit of good news, today’s decision does not impact current iPhone 4S Sprint users; we assume that this means their SIM card slots remain unlocked.

Source: SprintFeed