I believe that Scottsdale municipal airport is the only airport in the metro area with a dedicated helicopter frequency. All of the other airports use the regular tower frequency for all aircraft.
123.0250 is used by the medical helos to announce their movements around the Valley, and which hospital they are enroute to. It's also used by all helo pilots for situational awareness/airspace deconfliction.
When 2 or more Phoenix PD helos are up, you'll usually hear them on 123.0250, talking about any open incidents the fresh crew should be aware of that could request air support. Extended conversations will be taken over to 123.6500, which is their company channel.
I don't know about 123.4500, since I don't have it in my scanners. I've heard that it is used by fixed wing pilots as an informal air-air chit chat channel, but I don't know if it's used by local police/medical/media pilots as well.
John
Peoria