There are two ways to format your telephone numbers when sending an SMS blast:
North America:
North American numbers should be in a 10 digit format such as ##########. Any dashes, spaces, or parentheses will be removed automatically when the SMS is sent.
International:
International numbers require that a country code is used. For example, the country code for the UK is +44, and a UK number would need to be formatted like this in your SMS list: +44##########.
The country code must always be prefixed by a + symbol so the system will know those first few digits are related to the country code of the number you are trying to use for your SMS marketing.