Send SMS messages through our API

• How do I send an SMS message to a group via the API?
• How do I send Text to Speech messages via the API?
• How many receivers can I enter when I want to send out an SMS message via the HTTP API?
• How long can a text message be when I send it via the API?
• How do I send a test SMS via the API?
• In which charset can I deliver SMS messages and what should I take into consideration?