This page describes the standards and codecs used by TeleSign's Voice API.
The TeleSign Voice API supports the PCMU and PCMA codecs for voice calls. These codecs are specified by the G.711 standard.
TeleSign supports the RFC-2833 standard for DTMF, which is used both by the collect digits and send DTMF features.
TeleSign does not apply transcoding on DTMF.
TeleSign supports E.164. E.164 is an international public telecommunication numbering format that describes how to present phone numbers. You can read more about this format here: https://en.wikipedia.org/wiki/E.164.