Once the campaign is VERIFIED, the tab 3 - Add a New SMS Number to use for Composing Messages appears. It lists Active Phone Numbers for Composing Messages (numbers already attached, with a Compose a New SMS shortcut) and, below, a Select a SMS Number dropdown of your active numbers that are not yet attached with an Add This Phone Number button. If you have no numbers left to add, a Buy a New Phone Number link takes you to the Numbers page. In practice Sprwt also attaches any active, unattached numbers automatically the first time you open the page after verification, and switches your account to send through the messaging service as soon as at least one number is attached. Adding requires an approved brand, a verified campaign and an existing messaging service; otherwise you get a message such as "Please check your campaign use case status".