Record two minutes of ringing, so that depending on the type you record and the phone of the caller they either think it's ringing normally or two minutes, or think it changed to a different sort of ringing and assume it's some weird technical thing.
Related anecdote, I have a friend who lives in NYC who told me he recorded his voicemail to start with the beep (or beeps?) that sound like a network confirmation of a call hang up, and then his "Please leave me a message" message a couple of seconds later, so that automated dialers would be fooled into thinking the call was dead, and hang up rather than leave a message. I'm not familiar with American phone systems and am not sure if this is a story from the past (he's certainly been hacking systems for longer than I've been alive) or if it's still useful to this day (I'll pay attention if I ever call and get his voicemail, but we don't speak often).
Related anecdote, I have a friend who lives in NYC who told me he recorded his voicemail to start with the beep (or beeps?) that sound like a network confirmation of a call hang up, and then his "Please leave me a message" message a couple of seconds later, so that automated dialers would be fooled into thinking the call was dead, and hang up rather than leave a message. I'm not familiar with American phone systems and am not sure if this is a story from the past (he's certainly been hacking systems for longer than I've been alive) or if it's still useful to this day (I'll pay attention if I ever call and get his voicemail, but we don't speak often).