For all standard phone numbers worldwide, Twilio strongly encourages all our users to follow E.164 formatting guidelines. However, these guidelines do not apply to messaging short codes. Short codes do not have a country code, or a leading "+" sign. In your API requests to Twilio, your short code numbers should be formatted exactly as they appear on your Twilio Console.
How should mobile users enter my short code number when sending SMS?
The user should input the short code number without a leading plus sign ("+") or country code. Adding a plus sign or extra digits to a short code number will result in messages not being delivered.
Google Voice users using the Google Hangouts mobile app for SMS may see a +1 added to the beginning of short code numbers. In current versions of Hangouts, this is only a display bug and does not affect delivery of SMS to the short code. For more details, see Can Twilio numbers and short codes send SMS to Google Voice users?
Notice: Some mobile devices, including iPhones, may automatically format short code numbers with a hyphen for better readability (for example, XXX-XX or XXX-XXX). This formatting does not affect delivery or the ability for these users to reply to your messages.