AT&T (T) has announced plans to roll out Wi-Fi calling.

The announcement comes only two days after T-Mobile (TMUS) announced that it will offer a Wi-Fi calling service for iPhone users.

Here are three things to know about AT&T’s plan:

• Wi-Fi calling will only be available to iPhone users at first.
• The carrier will not offer Wi-Fi calling right away.
• AT&T needs to set up VoLTE first in order to avoid any awkward transitions between AT&T’s service and Wi-Fi.

In addition to announcing that it will support Wi-Fi calling, AT&T took a hit at T-Mobile by saying its coverage is strong enough that it doesn’t need support from Wi-Fi calling.

T stock is down 1% Friday afternoon. TMUS stock is up 1.25%.