I am a VRS interpreter/operator. I do not BS. If I tell you that "all circuits are busy" then that is exactly the message I hear. Through experience, I know that typically happens when call volume is the highest. When I call someone FROM my cell phone I sometimes hear that messages.
If it's a fast busy signal, it just means that we're unable to connect for one reason or another. There could be a problem with the phone line of the person you're calling.
SOMETIMES if you call a cell phone and it doesn't ring at all and goes straight to voice mail, it means the person's cell phone is OFF. Asking me to redial 14 times won't help if the cell phone is off.
If it rings a few times and then goes to voice mail, the phone was ringing but they didn't answer for whatever reason.