What could be the use or application of SMS aggregators such as SMSLib or Kannel. Can I use them to send SMS's from my web server.
In case they can send SMS's will those be sent on a GSM channel or GPRS channel.
What would be the cost implications per sms on part of the customer and on part of my implementation process?
You can use those libraries/SDK's but you will still need to get a short code to send and receive SMS text messages to and from a mobile device.
OpenMarket offers this type of service as well as a number of software SDK's to implement your request. Also OpenMarket offers Premium SMS as well as MMS.
It's a lot easier then Kannel ;)
BTW if you just looking to send SMS via a web page and know what carrier the user is you might want to try the SMS gateway approach. It's using a special email address to send SMS to a mobile device, but I don't think they can reply to this type of message.