Tropo - Tropo is a cloud API for voice and messaging.
Twilio - Brings voice and messaging to your web and mobile applications.
Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Melrose Labs SMSC Simulator - SMPP SMSC simulator to test SMS messaging applications.
HotTelecom - Our company offers virtual phone numbers, toll-free numbers, PBX, SMS numbers and numbers for a registration more than 100 countries. Buy Now!