AT&T today announced a new iOS app for its business customers that will enable push-to-talk (PTT) features on the iPhone 4S and 5. The service will run over AT&T’s network but will also operate via Wi-Fi, which should provide improved in-building coverage for the service.

AT&T said in a press release that the service boasts large contact lists and the ability to combine PTT with mobile applications.

AT&T launched its PTT service back in November. The new offering is aimed squarely at attracting customers coming off Sprint’s iDEN network, which that carrier is decommissioning for use in its rollout of LTE. In September, Sprint said its PTT service, which runs on its CDMA network, now has more than one million customers.

AT&T’s move to bring PTT to the iPhone—which the company says is a first—comes as Sprint prepares to sunset its iDEN network. Sprint plans to use the 800 MHz spectrum left over from iDEN to supplement its LTE network on the 1900 MHz band. Sprint is on track to complete the iDEN shutdown by the end of June.

Sprint still offers PTT services, branded as Direct Connect, on some of its new phones.