the simple answer is yes, yes you can dial via IP address between to Polycom Real Presence Mobile applications.
But, only if you control the Network the call is made via.
If you are using a 3g or someone's WiFi Infrastructure then the call will not complete as Polycom utilizes the international standardized videoconferencing protocol that will require some network translation or forwarded ports.
This has been discussed on plenty of occasions within this community.
Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge. If you need immediate and/or official assistance please open a service ticket through your proper support channels. Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's