The march toward change in the U.S. mobile industry is continuing, with larger mobile providers now reacting to T-Mobile’s unlimited international data offering and the rise of mobile messaging apps.

AT&T today announced that it will be offering unlimited international texting on some of its plans. Starting this Friday, February 28, AT&T customers with a Mobile Share Value or Mobile Share plan will have unlimited international texting added to their plans.

The new offering will no doubt be useful for many AT&T customers, but the mobile provider is being strict about what type of messaging are covered under the plan. First, only SMS or MMS messages are covered under the plan. Second, the messages must be sent from the U.S. to other countries – the reverse is not subject to the unlimited messaging. Third, the messages must be received by a mobile phone of some sort, meaning that messages sent to tablets or PCs of any time don’t count. The SMS part of the plan counts for more than 190 countries around the world, while unlimited MMS messages can be sent to more than 120 countries.

In any case, none of this may matter since AT&T has reserved the right to restrict or terminate the offer if it finds “tethered messaging, excessive international messaging, or misuse.”

In addition to the messaging offer, AT&T also announced a new international calling package. The World Connect Value package offers $0.01 per minute voice calling to Canada, Mexico, and 35 other countries, including a majority of Latin American and Caribbean countries.