An SMS gateway is a website that allows users to send SMS messages from a web browser to people within the cell served by that gateway. ... The gateway acts as a relay, translating one protocol into another. Wireless network operators use SMS gateways to connect SMS centers (SMSCs).
Create new users and allow them to use SMS Gateway using their mobile phones. User created by you can use their Android device as SMS/MMS Gateway by installing Android application. As an admin user, you can see all the messages they sent. You can limit number of devices user can use with their account.