Sonim Technologies said today that the first push-to-talk over cellular (PoC) system went live commercially today over KPN’s GPRS network in The Netherlands, bringing to a close a four-year development cycle intended to give GSM operators the same walkie-talkie capabilities as Nextel.

Based on the Open Mobile Alliance’s standard, PoC uses SIP-based VoIP to initiate and maintain PTT sessions over a GPRS network, making it available to a majority of the world’s operators. Setbacks in the technology’s development kept in the trial stages for years, however, and U.S. carrier Cingular tested the technology but eventually rejected Sonim’s solution in favor of a proprietary solution built by Kodiak Networks.

Several carriers, however, are expected to go live with PoC solutions in the coming year. Nokia has sold several systems in Europe and Ericsson has landed a PoC contract with Softbank in Japan.