I have a web application and I would like to enable real time SMS notifications to the users of the applications. 
Note: I currently cannot use the Twitter API because I live in West Africa, and Twitter doesn't send SMS to my country.
Also email2sms is not an option because the mobile operators don't allow that in my country.
The easiest way to accomplish this is by using a third party API. Some I know that work well are:

restSms.me
Twilio.com
Clicatell.com

I have used all of them and they easiest/cheapest one to implement was restSms.me
Hope that helps.
How do I enable SMS notifications in my web apps?