So I successfully deployed Skype for Business 2015, registered our PIC at https://pic.lync.com, successfully ran Microsoft Remote Connectivity Analyzer at https://testconnectivity.microsoft.com/ (says it tests only Lync but works for SfB as well).
An internal Skype for Business Client can successfully search the public Skype directory and add Skype accounts. However, the 'We've sent a contact request." part of the screenshot below never happens. In fact, the Skype user never gets a contact request.
Also, Skype Users can't search for our federated Skype for Business accounts in the public Skype Directory.
So obviously I must have missed something while deploying SfB, but I can't figure out what. I double and tripple-checked every deployment guide I could come up with, nothing. Double-checked our firewall ACLs as well, all good.
Any ideas?
This is very much downplayed for some reason, however the fact is that successful public Skype connectivity entirely depends on having the right Skype client version.
Basically, if you want to connect with a SkypeID (non-Microsoft account) user - which is the new advertised capability with Skype for Business server - you need the remote user to have at least Skype 7.3 on Windows 7 and above. Also you need that if you want video.
However, if you're connecting to Microsoft Account user (older capability, already present in Lync 2013), any reasonably current client (e.g 6.4+ on Windows) works, including OS X and mobile clients. The video won't work without 7.3 on Win 7, though.
If you don't have the required client version on the public Skype side, the Skype user won't receive any trace of the invitation, exactly as you're describing.
A good way to check is to try to search for your corporate domain user from the public Skype client (you need to enter the full [email protected]). If the search returns anything, the federation is supported with this OS/Skype client version/Skype account type.
Note: Microsoft has promised to add full SfB federation support to the OS X and mobile public Skype clients. No timelines, though.
Edit: the only reference document on this matter that I'm aware of is this: https://technet.microsoft.com/en-us/library/dn705313.aspx Specifically, the second last table. However, it differs in some points to my answer. My information comes from extensive first-hand testing. The official documentation on Skype federation, in my opinion, is severely lacking.