If it's about people sending SMS's into your central system, or your staff sending SMS replies back to mobile phones, you might have more luck doing a Google search for 'SMS Marketing' or 'SMS Gateway'. There are hundreds of PC apps, web apps and managed service providers in the market. The B2B team of your mobile phone provider may also be able to recommend some names.
Unless you have the skills to develop and support the solution internally, tou may want to consider whether a web based solution would be more practical. It may also depend on your capex/opex situation and the volume of traffic.
Whichever solution you go for, the interface to the SMS Gateway provider will be important. Pricing will depend on volume, the destination of the mobiles (international or domestic?), etc.