The settings for your account can be found in Organisation -> My Account
Configure the country code, this will be (United Kingdom (+44))
Type in your mobile phone number, then click on the "Confirm" button. Click the "Save" button.
This will send an SMS to your mobile phone with a unique code, this when typed in will open up the "Sender Options" in the Communications page, allowing you to change the Subject and Sender details.
If the confirm button does not respond then click on the save button.
The verification code will be sent to your mobile phone number by SMS, type the code in when prompted, then click on the "Activate" button.