This device is not GSM-based or SIM-based. You need to keep the phone connected with this for its working. The distance between the phone and device is 10 to 15 Meters.
This device is not having the auto call pickup function. 

Any one can call from any distance to the connect phone and the user will be able to answer and talk using the neckloop device and Hidden earphone.

Package includes -
1 Neckloop
1 Electronic earpiece
2 earpiece cells - Model SR416SW 337 1.55 V ( one earpiece will work up to 4 hrs ) -

You will have to change the cell after every four hours How it works - This product needs a Bluetooth compatible phone/Device for its work. - You can play any audio/video and hear the sound using this device - Volume regulators available - Play/ pause/ forward/ Backward buttons available Battery backup - Calling 4 to 5 hrs Standby up to 14 days Extra Features - Active Pairing With active pairing the will automatically search for Bluetooth phone or device and connect to it. 100% Clear calls. Audio Technology optimized for high-quality calls. Stream from your phone.

Music and GPS Directions. Weight:10g/ Bluetooth Ver.3.0+4.0 EDR

 
Cautions - 
Don't use this earpice for longer time. 8 to 9 hrs is maximum use time since it's electromagnetic ways might harm if exposed for longer durations. 
Never sleep with earpiece in your ear
Do not insert forcefully. Don't push the earpiece as they might harm your ear canal/drum. 
The buyer shall not use the product for any illegal purposes and shouldn't permit anyone to use the product in any kind of unlawful activities. We promote our products for betterment for our lives not to go against law, or humanity.