AT&T's new push-to-talk service will go live in November after the operator widened trials of the product earlier this year.

Customers can now register for the "enhanced" PTT solution, an upgrade from AT&T's basic walkie-talkie-style service.

The HSPA-based PTT service is being positioned as an alternative for customers being forced off Sprint's iDEN network ahead of its scheduled shutdown next summer.

"Is your business using iDEN push-to-talk, and looking for a better alternative that will be around for the long run?" AT&T states on the website for its early registration program.

The operator is also aiming to attract Private Mobile Radio users ahead of the FCC's narrowbanding mandate, which is expected to result in widespread replacement of the radio systems.

In June, AT&T doubled the number of eligible participants in its PTT trial.

AT&T's PTT product sports a number of added features, including calling up to 250 people at one time, presence indicators to show which contacts are available to talk and the ability for supervisors to override PTT calls with their own messages.

Compatible devices can download the PTT client without special configuration.  Apps, GPS and cameras can be used without interrupting PTT calls. In the future, AT&T plans to add location-aware dispatching software to the service, an addition that could be attractive to taxi and delivery companies.

Up to six phones will be made available when the service launches in November, AT&T said. Its advance registration website currently lists five phones, the Samsung Rugby Smart, Galaxy S III and Galaxy S II Skyrocket, and the BlackBerry Curve 9360 and Bold 9900.

Businesses can pre-register for the service now for discounts on PTT smartphones, or they can activate a beta version of the PTT client free-of-charge until it goes live in two months. Potential customers can also enroll in AT&T's charter program, which allows businesses to check out the service before buying.

Sprint is replacing its customer-losing iDEN network with a CDMA-based product, but has struggled to shift its PTT customers over to the new service. It lost 3.26 million iDEN customers between the second quarter of 2011 and the same period this year. At the end of June, Sprint had 3.14 million postpaid iDEN customers and 1.27 million prepaid iDEN customers.

CEO Dan Hesse told investors last quarter that Verizon Wireless has reaped the lion's share of those defections with its CDMA PTT product. During a typical year, AT&T acquired about one-fifth of the iDEN customers leaving Sprint, while T-Mobile gleaned about 5 percent, Hesse said. Sprint itself recaptured on average just 25 percent of its outgoing iDEN subscribers.

Sprint plans to use the 800 MHz iDEN spectrum for its LTE network, which currently uses its 1900 MHz holdings. It plans to use carrier aggregation to bond the two swaths of spectrum into a single channel for its LTE network.