The issue is that company pays a high price for such convenience. Customers of GSM carriers pay a high price for the pleasure of being able to contact people on their mobile phones. One reason for this is that calls from a fixed line to a mobile phone must pass via a PSTN to mobile connection facility, commonly known as a Mobile Telephone Switching Office (MTSO). When delivering calls from fixed lines to mobile phones, the PSTN operators must pay for this overhead. These expenses are passed on to fixed-line customers in the form of higher call prices. The 2N VoiceBlue Lite and 2N VoiceBlue Enterprise are GSM gateways that support Voice over IP (VoIP). As more businesses learn about the advantages and benefits of IP telephony, more firms are electing to replace their traditional PBXs with IP telephony solutions. The issue is that, until now, businesses that wished to use GSM gateways (Fixed Cellular Terminals) in their IP telephony settings had to use analogue gateways that were built to function with classic analogue PBXs. Because analogue signalling must be translated to VoIP signalling in order for this technology to work in an IP telephony environment, it is challenging to implement. Because the two technologies were never intended to function together, this becomes inconvenient and costly.To communicate with an IP PBX, the Voice Blue Lite (www.2n.cz) gateway features a pure VoIP interface that uses the Session Initiation Protocol (SIP) and Real-Time Protocol (RTP). For most IP telephony providers and environments, SIP is quickly becoming the industry standard. Many advantages are realised by employing native VoIP protocols in an IP telephony environment rather than cobbling together a solution with analog equipment.