There are a number of products that might help. ‘nowsms’, ‘clickatell’, ‘SMS gateway Enterprise’ and so on.
Also depends on if you need ‘two-way’ sms or just the ability to send tesk to mobile devices, without the requirement to get a reply.
If you want two-way traffic, you can either have an SMPP link out via your firewalls to your mobile service provider or at the very basic level, just a mobile phone attached to the pack of a PC, to send the text messages.
Finally, you may not want to build and manage an SMS Texting gateway yourself, you could consider a hosted service, where you can expect to pre-purchase texts in blocks of thousands.