Looks like they actually send you a jailbroken iPhone physically in the mail to enable iMessage. Not sure how scalable that is.

How exactly does this work?

I find this interesting as it raises so many questions:

Do they just give away free iPhones, or reset it for each user and have them mail it back? What if it gets lost / damaged during shipping? How do they cover the costs of this?

I may be wrong on the physically mailing you the iPhone. It could be that they ask for your Apple login and just log you in to a jailbroken iPhone on their premise.

I think the news they'll generate from it alone will be worth it.