It's a shame that their networks are incompatible, and there is probably a lot of overlap in the service maps of these two companies.
My wife's entire family uses Yahoo mail. Her mom is always bugging me by asking me how to do this or that in Yahoo mail, despite my best attempts to explain that, while I have five or six email...
Android has historically been laggy, even on high end devices. Either these things would have awful performance, or more likely, Android has been stripped to bare bones for performance.