A DHC-8 diverted to a nearby airport when the flight crew was unable to change frequencies on their VHF com radios.

Narrative

I was pilot flying. During our climb to 15;000 feet we started hearing static on the radios. However when ATC contacted us; we were still able to hear them as the static went away during the communication. When center gave us a new frequency; we were unable to switch frequencies. As the radio head froze; the dials were doing nothing. We tried switching it through the RNAV; but for a while the frequency screen wouldn't appear; all we were getting were frequency bus error messages. Comm 2 was already on the SELCAL freq before it froze; so we could communicate with maintenance control via SELCAL; I also noticed that my navigation radio was lagging behind with the dials; and I couldn't receive any kind of navigation signal. It was VMC and the RNAV was working with navigation functions. We were able to start changing freq via RNAV for a short while until it froze again. We then decided that we needed to land somewhere besides our destination because we would have no way to communicate with them and we would be out of radio range with the frequency we were already on in a short while. ZZZ was only about 20 miles away so we diverted there; coordinated our approach and landing with Center who was communicating with ZZZ Approach and Tower. After safely landing and taxiing to the gate; we contacted and coordinated with ground personal to deplane the aircraft; contacted maintenance control; fixed the problem; the logbook was signed off and we continued to our original destination. We first noticed that it was frozen when Center gave us a new freq and we were unable to switch; before that the frequencies were changing fine.