Lync, when it first released a mobile client did not support voice over WI-Fi. In an article I stumbled across today, I was reminded of why that was. Adam Ghent, admittedly a couple of years ago, laid out some of the reasons why VOIP Over WiFI was not quite the holy grail that some Lync competitors saw it as being! IN particular, Wireless is not all that good with real time media, combined with the fact that most wireless deployments were carried out without regard for real time media.
Now since this article was first published a couple of years ago, Microsoft has announced WIFI support for VOIP so you CAN do it, but again the question is whether this is a good thing. If you are deploying Lync, while VOIP over Wifi may appear attractive, consider your wireless infrastructure carefully. Does it support QOS? Can a voice call be transferred fully if the client moves between access points? And if you have roaming support turned on – what happens when the phone moves out of wireless range – hint it uses data over the telephone which for some plans can be considerably more expensive than using GSM et al.