In the majority of cases, mobile phone number data coming from external systems is not ideal for SMS delivery. For highest reliability and to be able to route correctly a mobile number should be formatted in international format E.164 Normally however a number is stored in a CRM or contact database in local format, with spaces, hyphens and other types of unwanted characters that can cause a delivery to fail. The format-number call is used to sanitise a number by combining the country and the number. eg.

Australia 0438 333 061 will become 61438333061 New Zealand 0212172782 will become 64212172782 USA (281) 869-1226 will become 12818691226