It's no different than using a telephone extension or using a tape recorder at the end of a phone call. Both of which are protected exclusions because as stated during United States vs. Harpel "The recording of the conversation is immaterial when the overhearing itself is legal". This also makes sense when you remember these laws were created to prevent eavesdropping and you cannot eavesdrop on yourself.Did you not even read the case? I'm not understanding how this case is relevant to your situation(I could be remembering wrong but I thought you're in trouble for recording 1 on 1 conversations you had with people)
1) A telephone extension is an exclusion under certain conditions, yes. However
"Similarly, we do not feel that a telephone used in the manner contemplated under the facts of this case is employed in the ordinary course of business. Harpel qualifies for no exception which would bring him without the purview of 18 U.S.C. 2511."
The court ruled he didn't fall under the phone extension exclusion in this case.
2)
We agree with appellant that the recording of a conversation is immaterial when the overhearing is itself legal. It is the means whereby the contents of the conversation are acquired that is crucial.
They're saying the fact that he recorded a conversation in this case is irrelevant if he legally overheard a conversation. They go on to say in the next sentence the only crucial point is how that conversation was overheard, was it legal or not. The case is only saying that you can record a conversation that you legally overhear.
3) The court affirmed the lower courts decision, he was still found guilty.
How does this case prove that telephone extensions are an exclusion when in fact the court ruled the guy illegally used one and that the audio device WOULD HAVE been fine if he legally overhead it? I don't understand what this case has anything to do with you. The case is a third party overhearing case while yours is a private conversation you had with someone else. And in Maryland it's illegal to record someone without their permission.
Edit: I don't know what you're actually charged with btw