One of the main problems for us was that "can I call this guy if I know he's at home?".
Our company (read: me) did initiate Microsoft Lync as our main chat/call/conferencing tool. To us, this program has been a fantastic tool for getting presence info. If the guy is available then just call him. We have also incorporated our mobile phones into Lync, as our Mobile service provider sports this. This means that we can see "Mobile phone active" when we check the status of our colleagues, and the status is then set to Busy as well. Also, it synchronizes status to meetings in Exchange calendar for the users, giving info to others about their availability.
This presence info seem to be the key for contacting people commuting. It's simple: you never know what people are up to. It's that simple. Being included at home is hard. But easier if people know if you are available.
I guess you could use other tools as well, however none of them would do all that Lync do at present time.
I see now that I've written a somewhat commercial for Lync now, but I really do not care as it's been very helpful to us.