Control from cell phone

I’m looking for a solution for operators to control access controls from a smart phone. Right now operators that have to do rounds and have work orders in a good size plant have to walk back to the control room to let delivery drivers and guests into the plant. Im looking for an option where they could dial a number to control a digital output or second choice would be using something like IDEC has an affordable webserver function where you can design a webpage to view and/or control on a smart phone, tablet, etc.

You need either GSM based products or IOT based products.