Divert PSTN to GSM / Call Divert The CTM3000A call divert box is a call diverting device which provide the ideal solution to eliminate the cost of diverting calls from a landline to mobile phone. The call divert box will replace the traditional call diverting service for small enterprises or SOHO to reduce the high call costs from PSTN to GSM.A call forward box connects the extension port of PBX / PABX with GSM networks instead of PSTN and it enables all incoming calls to be automatically forwarded to their mobile phone or fixed phone without incurring high network diversion charges and landline to mobiles call costs.