In fact, it appears that certain South Metro units have one radio assigned to METCOM-2 and one for Littleton Dispatch. Why are certain South Metro units assigned to Littleton's dispatch channel, and which units typically get so assigned?
I believe a lot of the crews on the border of the South Metro/Littleton border will proactively scan the Littleton channels, but otherwise I see a lot of radios switching between the two channels as needed. As for the specific units that Littleton constantly dispatches for their calls, well it's basically all the South Metro stations are free game. Both agencies as well as dispatching centers have what I consider beyond excellent working relationship as you can very often hear MetCom-1 monitored in the background for Littleton Dispatch and hear Littleton Dispatch in the background for MetCom. Both dispatch centers quite often dispatch their side of the response as needed within 30 seconds of the initial dispatch as opposed to many of the other dispatch centers in the area which can have a dispatch delay as long as 4 minutes while information is given over phone or Metro Net.
Units I have recorded responding on Littleton Dispatch for the past 2 days are Medic 31, Battalion 32, Tower 32, Medic 32, Engine 33, Medic 34, Medic 37, Engine 38, Medic 41 (likely for Cunningham), and Medic 42 (likely for Cunningham). On the reverse, South Metro also requests Littleton units as needed and in the past 2 days I have seen Littleton's Squrt 12, Engine 15, Medic 15, and Engine 17 running calls for South Metro. Cunningham also responds for South Metro as needed, but I haven't sorted out their Radio IDs as of yet. I definitely remember hearing Engine 63 and Medic 63 running for South Metro sometime in the past week.