Microsoft is in the process of retiring Skype for Business and replacing it with a new product called Microsoft Teams, so you should use that instead. You don't need a server, and you can sign up for free here:
https://products.office.com/en-us/microsoft-teams/group-chat-software
If you have any more questions about Microsoft Teams, the best place to ask them is in /r/MicrosoftTeams.
See attached. It's a little old but should still work for your needs. For example, CWA no longer exists.
For learning/keeping up with Lync /Skype for Business download UC Now for Android or Windows Phone. Search for it in the store.
Here's a couple:
http://www.intermedia.net/products/lync-secure-chat-and-conferencing/pricing
http://www.rackspace.com/skype-for-business/
If you can't find a good standard host, my company can set up a Skype for Business system in a local ISP for you, customized the way you want it.
Here is an alternative skype4b iOS app
https://itunes.apple.com/us/app/sky-for-lync-skype-for-business/id658945153
It has no moving parts
Android too
https://play.google.com/store/apps/details?id=com.wync.fisil