GSM4K-1S/4G. The Videx 4000 Series GSM4K-1S/4G “entry-level” surface mounted audio kit is a totally self contained GSM door entry system kit. There are also auxiliary input and outputs. This kit includes a door panel, Psu & antenna, requires only a Sim card, and can be programmed by either SMS or PC Software.. 1 way surface audio gsm. Diversion to second number when first number is busy / not answering. Dial open, balance check & signal strength checking facility. Totally self contained (only requires an external power supply and antenna)