When you send a URL in an SMS, the URL will automatically be shortened to reduce the number of characters used and to make your message more presentable on a handset. This also allows you to track whether the link has been opened by each recipient and that will appear in your reporting.
If you do not want your URLs to be shortened, you can deactivate the shortening service by:
1. clicking on the settings cog next to the green settings module in your SMS template: and
2. selecting "No" under Shortlink SMS.