Sorry for the geek-speak
Lync is Microsoft's Voice Over Internet Protocol telephone system, which has Internet messaging, video conferencing, desktop sharing, file transfer and Presence status all in one small app. It works really well and you don't have to have a phone to use it, a simple headset connected to your laptop works great.
Office 365 is Microsoft's Cloud offering of Office and the suite of tools associated with it.
I decided to use Office 365's Exchange email services as they are replicated across multiple remote data centers, instead of our single Exchange server we have on-site, as it is a single point of failure.
I've been systematically addressing all of the single-points-of-failure in our IT infrastructure by building in and adding redundant key pieces of network hardware.
i.e. We have two Internet Service Providers, connected to dual/redundant firewalls, connected to redundant core network switches, with redundant domain controllers and redundant Active Directory servers.
I've moved all of our key servers from physical stand-alone servers to redundant VMWare servers, located in separate IT rooms at our various locations as well as a third party data center.
What it boils down to is, that as long as we have Internet access, we are in business and up & working.
Again, sorry for the geek-speak, but you asked!