I need to get a static IP block and have a couple of questions

 I run an old-school BBS system that can send internet email, as well as some emails that go to other BBS systems, but that requires outbound port 25.

Port 25 is blocked by default.

Secondly, what changes at my location? Do we keep the protection that our AT&T service is providing? Do I retain all of the parental controls that I have now? Does our AT&T-supplied equipment change?

Nothing changes. There are no changes in your AT&T provided Gateway just some additional configuration settings. Yes the "limited" parental controls remain the same.

Dave

To my knowledge you are required to have a business account to have port 25 unblocked.

The smallest static block is $30 per month which is a block of 8 with 5 usable.