SMS integration API for ecommerce website


I’m developing website based out of India for global market for a niche e-commerce portal where buyers & sellers platform.

I wanted to integrate SMS notification for members who have posted products for sale in the website.

My initial analysis where I could find lot SMS bulk Domestic package offerings from companies within indian gate way which is relative less and for international SMS package, we find that its expensive.

Please do suggest, what is the best way to manage both domestic and international Users…
-Please suggest any preferred vendor
-Also I do find of websites which we can post international SMS…Not sure, is their a way to integrate this website API"s to my e-commerce portal to send international SMS.
-Is their a way to buy local sms in that preferred country locally(international sms -USA) locally and use them based as international SMS…Not sure, whether this is feasible option.

Please do guide me How to go about to manage both domestic and international User (Users mainly from USA, UK,Germany,France,Singapore,Spain,Malaysia,Australia,Italy, UAE).

Your input will be appreciated.