A method and apparatus for improved resource allocation in ad hoc group calls includes receiving a request for an ad hoc group call with another push-to-talk (PTT) system between a plurality of subscriber units comprising a plurality of Project 25 (P25) subscriber units; allocating resources with the another PTT system using an Inter Radio Frequency Subsystem Interface (ISSI) network to network interface (NNI); and identifying the ad hoc group call as a single logical call for the plurality of P25 subscriber units on the ISSI NNI. This can also include allocating a single channel for the plurality of P25 subscriber units identified as the single logical call.