I considered that too but wasn't sure. There is a Rogers site VERY close to this site and is in a prime location, highly elevated, I can't see them sharing on this tower.
Telus has no towers here, but as for 'Mike' service I can't say much because I don't really know anything about it.
The 2-way radio sounds very possible, but that is not a new technology, so why would they have just made the upgrade now? Up until this point, BellAliant sites around town for the most part have been one set of antennas, all the same type.
I've seen this exact configuration on another BellAliant tower here as well, and more being upgraded. They're looking very ugly now compared to before!
I do like the idea of site sharing, it seems to be very popular in other places, especially like you said, on really large sites.
The only two carriers here being Rogers & Bell, Rogers has VERY few sites in the province compared to Bell, so they have nothing to share here
Still meaning to get a pic of the antennas installed.. will try to do that soon.. and maybe some other upgraded sites if I can.