Only relevant to self-serve customers. For other packages, Clickatell does this on your behalf.
Navigate to Products & Services -> Channels -> SMS.
Click +Activate channel.
This adds SMS as a channel on the My Workspace tab.
On the My Workspace tab, click the SMS card to open your SMS channel management page.
From here, you can:
Add new SMS setups.
View and manage your SMS setups.
View, manage, and purchase new long numbers and short codes.
View, manage, and add test phones.