Are the wireless carriers (ie Verizon, AT&T, etc) complicit in the manufacture of these products? It would seem to me that those companies would regard the use of a "Stingray" to impersonate one of their towers as an unauthorized intrusion into their network.

Is it possible for wireless carriers to modify their towers so as to make them less susceptible to spoofing? If so, why don't they do so?!

I'm not a telecom engineer so this is not my area of expertise.