Well, I can understand why some actually consider a message "hey, can we talk" more polite than simply calling without asking first, especially for developers. After all, they may currently be in the middle of doing something and would prefer not to be disturbed. OTOH, a message is already a disturbance, and most of the times checking your calendar should already give someone a hint about whether you are busy or not. Either way, providing a hint of what you want to talk about, e.g. "hey, can we talk about that spline reticulation issue?" is of course much better.