Push-to-talk (PTT) technologies date back to the advent of the telegraph and more recently have been the domain of traditional land mobile radio (LMR) networks. The past few years have brought about a resurgence in PTT as a service offered by commercial providers, driven first by private subscribers and, increasingly, by organizations such as law enforcement agencies that traditionally rely on LMRs. This technology, today one of the growth areas in the communications industry, has received little attention in the scientific literature. In this article, we discuss some of the emerging technologies (voice over IP, CDMA used in 2.5G/3G systems) that relate to today's PTT service. We also discuss the market and financial implications of commercial PTT on current LMR deployments.