Push to talk PTToc app for iOS and Android

I’m looking for an experienced freelancer to build out a Push To Talk Over Cellular (PTToc) app for both iOS and Android. The PTToc app must have a user account system, and utilize Voice, text, as the primary user interaction. It should make use of the latest technologies to ensure a fast and reliable experience for users. I’m open to comments and suggestions with respect to the feature set and design, and am looking forward to hearing your ideas about how to make the app both visually appealing and technically robust.