Here is the official response from Clickatell.com:

Thank you for contacting Clickatell.

Recent changes have taken place in the US marketplace with regard to USA messaging, and it is now requested that all existing SMS traffic, including mobile terminated (MT), alerts and notifications, etc., now be run over dedicated US shortcodes. Messaging to the US is currently running perfectly, but we do foresee that in the near future there will be a strict control on all messaging.

As a temporary solution, Clickatell currently routes all USA traffic (for clients who do not yet own their own Shortcode) on a registered and approved Shortcode, so messages will not get blocked. We propose that customers prepare themselves in advance and startto activate a dedicated Shortcode as soon as possible.

More information regarding obtaining short coded numbers can be found at – http://www.clickatell.com/brochure/us_shortcode.php

After checking with numerous aggregators, and pseudo-aggregators, this appears to be the consensus.

There is one company which has not published this requirements, yet. Quios.

Though, I expect the same response from them shortly.

In the meantime, I have compiled a list of over 250 Email to SMS addresses, covering most carriers.

Hopefully, I can scale our project quickly, take advantage of volume discounts, and offset the financial impact of leasing a CSC.

Before that happens, I need to receive a crystal clear explanation of what can get your CSC shutdown, and if there is any recourse against false complaints or potentially malicious acts.

This new barrier, coupled with the play for tiered internet access, companies like SBC are making, could make it difficult for startups and small tech companies to do business in America.