The short answer: you can't.
The thing about sending messages from a TFN, is that they need to be verified for a specific use case first. During the trial experience, we supply you with a pre-verified TFN with an approved use case for sending specific templated test messages to yourself. That way you get to experience all the awesome features of the Hub and get a feel for how it'll suit your business needs, as well as your customer's messaging experience, without the commitment. When you're ready to start sending to other numbers, all you need to do is upgrade to a paid account and you're good to go.