Once a lead has been set up with a mobile number and the SMS setting have been enabled, texting is a great way to reach them.
First, send an SMS Opt-in Message. Once the lead has opted in for receiving text messages you now can send a message to the lead. If the message is longer than a sentence or two the whole message may not show in the Activity history of the leads data.
To see the full text you need to go to the Leads Details History.
Next, go to the SMS section to see the complete text messages and responses from the lead.