With the latest UCS software are you able to use both OpenSIP and Skype For business on the same phone, as long as the phone is licensed for S4B?
Stating the latest software does not help others when finding this post in days, weeks, months or years to come as they do not know what software mentioned was current at the time of writing.
Please therefore always post the exact complete build id.
Therefore the Polycom VoIP FAQ contains this post here:
Question: How can I find out my SIP or UC Software Version of my Phone?
Resolution: Please check here
and to answer your question the Skype for Business FAQ contains:
Jan 25, 2016 Question:How many Lines can I register using Polycom phones with Lync Server / Skype for Business server ?
Resolution: You can register only one line when LYNC / Skype for Business is set as the base profile on the phone. The Polycom Trio platform has a hybrid feature for 3 different lines. The first one must be Skype for Business / Office 365 and more details are => here <=
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services