You can send text-to-speech messages with our API, you can find a further explanation on how to do this in our Developers Documentation for Voice Messaging.
This works internationally for both mobile and landline numbers. With text-to-speech (TTS), the user always gets a phone call, whether to a landline or a mobile phone. If the receiver answers the phone, the sent message will be spoken by our text-to-speech computer. You will also receive delivery reports for text-to-speech messages.