"The ability to set your outbound Caller ID to any number" - This is an attribute in our <Dial> element which allows developers to build systems that initiate calls from the phone number of their choosing. E.g. I can initiate a call to Bob from phone number (555) 555-5555. I.e. it doesn't have to be from my TelAPI number.
"Reverse carrier lookups on phone numbers"- TelAPI provides a way to look up the carrier of a phone number via the REST API.
"Flat-rate unlimited inbound calling to your TelAPI phone numbers" - For businesses/users racking up the voice mins per month, they can opt to buy an unlimited inbound channel for $27/mo instead of paying min/mo rates.
"Voice and audio effects on your phone calls" - These allow developers to modify the pitch and tone of a caller's voice (and basically make their voice sound like anyone they want). We also offer an ambient noise feature to add background noise to calls (e.g. city traffic, poor reception, etc).
"Private number Caller ID unblocking" - Upon receiving calls from blocked numbers, users are able to ascertain the callerID. Our parent company TelTech developed an application called TrapCall which takes advantage of this.
"Premium transcriptions with human processed dictation Speech recognition" - We offer four different transcription services (varying based on a developer's/business's needs) which allow consumers to record their calls and have the dialogues from the calls captured in text.
Thanks for the question!