If the person is in more than one opt in keyword then it goes to either all campaigns or it goes to the last communicated campaign.

Not ideal of course. Best to have geographically isolated short codes to minimize this. But it's better to be FCC compliant.

The $500/month short codes were for unique. That is the actual CSCA pricing. When I do mobile banking projects, we typically pay that directly to CSCA and then we pay our SMS Gateway provider (commonly used Syniverse in the past) separately for usage.

http://www.usshortcodes.com/get-a-sms-short-code/sms-short-c...

I'm a pretty risk-averse person and I can't imagine in any way the FCC cracking down on the use of long codes for legitimate two way communication with an existing customer. On the other hand, using long codes for mass marketing campaigns and you'll probably be shut down by the carriers and possibly sued, no FCC action required.