Line2 - Line2 adds a second phone number or complete cloud business phone system to smartphones & computers that's robust yet affordable. Buy online or get a custom quote.
Twilio - Brings voice and messaging to your web and mobile applications.
Phone.com - VOIP Business Phone Service + Virtual PBX
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Voxbone - Fully compliant, enterprise-ready voice and SMS on demand. Build local presence on a global scale with elastic SIP trunks and phone numbers. Try for free.