There are sever threads on the topic of headsets in the tandem forum. The currents designs have excellent battery life, work of longish distances and are compatible with the latest bluetooth specs - interface with Smartphones, etc. I have an interphone F5 and am very satisfied. Cardo makes a number of such headsets, some specific to bicycles. The noise canceling is now really excellent.
I would start by looking at these various websets. The use of the term Walkie-Talkie is a bit different and sounds like something handheld which is a completely different paradigm.