My office is room G.15 in the O'Reilly institute, which is at the East end of the campus (that's the "back" of the college, near to the Science Gallery). If you're coming to see me I suggest you put it in my calendar to make sure I'm there and available -- I'm trying out this online calendar which let's you confirm a time that suits us both.
You can telephone me on +353 1 896 3629 (this number has voicemail, and I do check it).
You can Skype me at gdstrong. I don't usually leave Skype running, so putting the call in my calendar is the way to go. In theory we can use Facetime, too (but I don't have an iPhone so there's a similar need book it).
Good old snail mail works, too
School of Computer Science and Statistics
Trinity College, Dublin