Not likely to happen but if so more likely parings..
Apple-ATT (most established relationship)
Google-Sprint (both open source minded, strong existing relationships, Google already rumored to buy the Sprint HQ campus in KC, perhaps for Google Fiber HQ)
Microsoft-Verizon (the biz focused network)
Samsung-Tmob (the everything else network)
Dish was working with Sprint at one point to host on Sprint's new Network Vision infrastructure. Sprint is designing NV to allow MVNO infrastructure popped in, similar to a telcom hotel. But then they started to argue about invading frequencies, so may not happen.