Hello. I am setting up a digital receptionist with three options. Option 1: Transfers to voicemail for an extension. Option 2: Ring group. Option 3: Ring group. My only issue is that option 2 and 3 should/need to have members that are outside of the PBX. These are basically on-call type people for repairs. I know I could install the 3CX smartphone app on each of their phones, but I'm worried about the reliability of such a solution. In an emergency we would need to know that the person received the message. Is it possible to add external phone numbers (cell phones) to a ring group or am I thinking about this in the wrong way?