In these types of situations it doesn't even make sense to try and surreptitiously make a recording of the call. I routinely record _all_ calls between myself and attorneys, accountants, advisors, partners, etc. and after asking permission to record not a single time has any of these people denied me permission or even questioned why I would record the call. Most people even appreciate receiving a copy of the conversation afterwards as well. In business situations like this, asking to record a call for records purposes is not an anti-pattern and you shouldn't be afraid to ask the other party for permission.

Yes, in some states it's legal to record telephone calls with the consent of a single party.

I read his disclaimer as "I'm in a one-party consent state, but the person I'm talking to may or may not be - and I have no idea how admissible this would be as evidence but I'm pretty sure I'm not breaking the law."

This guide is slightly old (Last updated May 2014) but seems fairly comprehensive: http://www.dmlp.org/legal-guide/recording-phone-calls-and-co...

Depends on the state... and in one state, it depends on whether or not you know it's illegal. I forget which state, but it came up a lot in the news during the Monica Lewinsky affair.

I believe in some states it's a criminal offense to record phone conversations without the person's knowledge. So I would be very careful about doing this.