The system needs to have a gui to maintain a list of people who need to be contacted.
A list per alarm or a dynamic list such as a shift rotor and/or escalation and acknowledgement strategies.
So the reason I am leaning toward a Message service is that it probably has a more sophisticated Gui for managing these contacts.
This has been the traditional solution for use with soon to be redundant dialler systems. It brings about a whole gamut of other problems costs and operational issues to resolve.
Can you suggest one that takes relay inputs? That can be configured to send to various phone numbers.
Even the most basic stuff can action upon contact closure provided you have reliable volt free contacts available as triggers.
Most probably use RS232 which means I probably have to have additional hardware.
Possible less hardware. RS232 is a hardware standard. What protocol are you after, what data does the system have to contend with?
Also I wanted a solution that would work in different countries, mainly Asia, Oceania and South America so I was leaning toward a http based solution. Rather than one that uses a particular phone network.
GSM SMS will work directly in most areas, a web based solution brings a bout another level of complexity and another set of reliability and operational issues. You do not need to be tied to any single phone network.
I am looking for a finished add on, as my boss is thinking don't reinvent the wheel, but I think I wont find exactly what is required so I will have to do some development anyway.
It all depends on your requirements, you are talking a system, the contact sensing part is the easy part. You don't need to design hardware, that is reinventing the wheel. You are definitely looking at programmable units such as
http://www.glynstore.com/products/EZ863%252dQUAD%252dPY-Quad-Band-GSM%7B47%7DGPRS-Modem-Terminal.html But to some degree you will still be reinventing the wheel, I also have commercial solutions available, depends on your budget and application. PM if you'd be interested in evaluating options.