There are multiple ways to use an OBi with a mobile phone. First, from the mobile phone, you can call any telephone number which is associated to an service configured on the OBi (Google Voice™, SIP ITSP or analog landline account). By default, this will ring the phone attached to the OBi. Now, to take this one step further, go to the OBiTALK portal, and add this mobile phone's number to the 'Trusted Callers' section of the OBiTALK web site. Now, when this phone calls your OBi, the OBi Attendant will answer and the caller may direct the call to the attached phone (by pressing 1) or it will allow the mobile phone caller to make a new call (by pressing 2) or allow the mobile phone caller to make the OBi call it back (by pressing 3).