My application needs to verify phone numbers that are provided by the user. What is the absolute cheapest way to send an SMS to a phone? Which company/API should I go to? I'm not looking for a hack solution to send out 10 SMS a month kind of thing, I need to roll this out for a company that will be sending mass amount of verifications. But they want to do it at the lowest cost. (Each user will only need to verify once)
Sorry forgot mention the SMS needs to be international
I'd suggest using TextAnywhere:
They provide API's (C, Java, .Net, PHP etc) for several languages and provide a multitude of rates and packages depending on the volume of texts sent.
They're also very flexible with regards to payment - they do pre-pay, PAYG and fixed monthly limits.
We used them for a large-sized application to send alert notification messages and they were very reliable. They also give 15% discount for registered charities and academic institutions.