What are some alternatives?
When comparing Twilio and CALLR, you can also consider the following products
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Plivo - Plivo's Voice API enables businesses to build Voice apps to reach customers globally in 200+ countries. Try Plivo's Voice API for free. Instant Sign Up.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
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.
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
Textlocal - Textlocal is an app that allows for individual and group texting. It is designed for businesses that have employers and employees who need to communicate with each other, making it easier to announce group meetings and special announcements.