What are some alternatives?
Twilio - Brings voice and messaging to your web and mobile applications.
CrazyCall - CrazyCall is cloud based platform for sales and marketing teams doing cold calling, market research, information or loyalty campaigns.
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.
Nextiva - Business VoIP, cloud phone systems trusted by more than 150,000 companies. Powered by the leading cloud PBX VoIP platform, Nextiva is rated the best business VoIP service provider.
Bandwidth - Track your Wi-Fi hotspot usage. Zero configuration required. It just works.
PhoneBurner - PhoneBurner is a cloud-based power dialer to boost sales productivity