When sending SMS messages, the safest option is to send numbers in internationalised E.164 format, e.g. +642100001 and +61400010001.

Your account can be pre-configured to accept New Zealand and Australian formatting. This means you can submit NZ and AU numbers as a mixture of:
+6421000001 and +61400010001
006421000001 and 0061400010001
6421000001 and 61400010001
021000001 and 0400010001
21000001 and 400010001

International numbers will still require a leading + or 00, e.g. +447955554444.

The service is able to accept and strip any unnecessary characters, such as spaces, dashes and brackets.

For Voice and Fax messaging, see: Mobile Number Formatting for Voice & Fax