For the 2013-2015 infotainment system, you can pair multiple phones/devices to the system. But I think it can only be connected to a maximum of 2 devices at the same time.
When both phones are present, it will automatically connect with the one it last connected with. However, you also have the option to select what audio you want each of phones can contribute to the system. For example, you can select one phone to only have phone capabilities and the other to have just music/audio capabilities at the same time. This means you can have one phone who's calls will go through the infotainment while the other phone can be streaming music.
This is achieved through the bluetooth set up menu. You select the device, then can toggle which features you want to be enabled through the phone.
However, you cannot have 2 devices set up to share the same functions at the same time. One must be streaming audio and the other must be for phone capabilities.