It IS possible to send SMS text messages as part of a follow-up sequence from Infusionsoft!
There are a couple of tricks, though.
You can't use one of Infusionsoft's phone number fields because it automatically formats the number and Clickatell won't work right! But, if you just use a Custom field, then everything will be OK.
I made this work with Clickatell's SMTP API, by sending an email template like this:
user:xxxxx {Your specific Clickatell info}
password:xxxxx {Your specific Clickatell info}
api_id:xxxxx {Your specific Clickatell info}
to: 448311234567 {Insert the custom field data here}
reply:youremail@yourdomain.com
text:Meet me at home {This is the message you want to send}
I hope this helps. There's also more on the Infusionsoft Blog.