Our API plans offer everything you’ll need in an SMS gateway service. GREXT™ is a simple, pay-as-you-go, web-based message app. A simple, upfront, low-cost toolset with live support. Simple SMS for small apps and calendaring alerts. Add Ons Works on all carriers and reaches where shortcodes cannot. Connect to a Short Code reaching the U.S., Canada or international. The SMS Authentication PIN is popular for security validation. Text from your current business landline.