The issue is with the safari browser blocking the ability of the pop-up window to select send a SMS option.
To resolve this use Google Chrome Browser - to download this to your iPad desktop follow the instructions contained in the link below:
https://www.google.co.uk/chrome/browser/mobile/
When you click on a mobile number (not the mobile symbol) as shown below:
A pop up will appear as shown below:
Select the Send SMS option:
Type your text message into the SMS window as shown above. Click on Send to send.
To see a video guide on sending out as SMS please click here.