Today I tested Twilio the trial version. First you need to know about this cloud service:
Twilio is a cloud communications platform as a service company based in San Francisco, California. Twilio allows software developers to programmatically make and receive phone calls and send and receive text messages using its web service APIs.
About the trial version then this works with all customers:
Twilio offers a trial to all customers who sign up, which includes a free balance for you to experiment with. When your balance is getting low, Twilio will send you an email with information to upgrade your account.
About pricing , then you can find pricing for your desired number on our country by using this link to see local and from United States to your country.
You can interacting with via the REST Pricing API with Voice, Messaging and Phone Numbers.
Another option is the twilio-python library and can be used with Flask python module.
The most API come with product for all options: SMS, Voice, Authy, IP Messaging, Video, Notify, Taskrouter and tools.
The platform of this API include: Web, Mobile, iOS and Android.
Also not of this is all included. For example: the Twilio Programmable Voice SDK makes it easy for you to add voice-over-IP (VoIP) but just for: Android and iOS.
Another issue for you is to see if the ability to enable permissions to call almost any country by check limited number of countries.