@fgtrrt You just put the URL inside the SMS body text. Campaign will pick it automatically.
SMS doesn't understand HTML and hence it doesn't undestand the keyword href. It will consider it to be part of SMS text and send it as it is.
Just paste the URL and enable tracking, Adobe Campaign will pick it up.
Kindly note, that if tracking is enabled, Campaign can generate a very long tracked URL, replacing the original one you've added. It can increase the length of SMS which means you might end up billed twice the price from SMS vendor.