You can program up to four telephone numbers in the IO1058, whether they are landline telephones or cell phones. When a visitor arrives at the intercom and presses the button, it dials the first number. If the first number does not answer, the intercom dials the second number after the programmed "no answer" time is reached, and it repeats the procedure for the next numbers. So your visitors should always be able to reach someone and you won't miss important deliveries or visitors.
If you're using the IO1058 at a driveway gate, you and up to 99 other people can also use their cell phone as a gate opener remote control. The intercom allows up to 100 telephone numbers to be stored internally for users to be able to call the system for automatic entry. The IO1058 uses the caller ID of a mobile phone to identify callers, and when it identifies callers on the list, it activates its internal relay, which opens the gate. You can program in numbers for delivery drivers, landscaping personnel, friends, family members, or anyone who needs access to your property. All they have to do is call the phone number for the intercom and the gate opens. Since the system doesn't actually answer the phone call, it doesn't use any minutes from your cell phone plan. It is also more secure than typical wireless remotes since the gate won't open without the correct Caller ID coming in with a call.
To use this intercom you will be required to have a 4G GSM-based telephone service. GSM-based mobile phone service requires use of a Subscriber Identification Module (SIM), which is an integrated circuit card that securely stores information needed to identify and authenticate subscribers on mobile telephony devices.