The Session Initiation Protocol (SIP) has been chosen as the standard signaling protocol for the IP Multimedia Subsystem (IMS). SIP is a text-based protocol with messages often exceeding 1000 bytes in size, thus causing high call set-up delays on low bit-rate links.Signaling Compression (SigComp) is currently the only option cellular operators have for the compression of signaling messages. We study the performance of SigComp, showing that SigComp cannot achieve the level of compression required by Push-To-Talk over Cellular (PoC) services in the IMS. Furthermore, we propose an alternative compression mechanism, namely Template Based Compression (TBC), and show through measurements how we can achieve higher compression ratios than SigComp, satisfying the requirements for PoC on low bit-rate links.