Skype for Business will be deeper integrated into iOS and Android. So we will get rid of the barrier between app and cellular voice calls. *yey*
As-is
Today if you receive a call on your SFB App on your smartphone and receive a second call during that via GSM/celluar the SFB voice call is getting interrupted. And you cannot do much about it.
Future
Soon (October’16) you receive a call on your SFB app on your smartphone and a second call will not bother you any more as it now.
“[…]Skype for Business calls [than] work just like a cellular call on your iPhone[…]”