I doubt you will receive any help for doing this from anyone here.... certainly not from myself anyway... Helping you do so would be completely Immoral.
My apologies if any of this causes offense, I'm trying to be a civil as i can.
Apart from being completely immoral and a complete disregard for your sons reasonable expectation to privacy, what you are trying to do is almost certainly illegal for two reasons:
1. Recording of telephone calls / listening in requires both parties (your son and whoever they talk to) to be aware that the call is being monitored in most American states, or at the very least your son to be aware of it in some states, any spyware is completely useless to you if you tell your son as he will just use another phone to talk about anything he does not want you to know about.
2. The 'bug' feature that allows you to listen to what the phone can hear around it can/would breach other peoples reasonable expectation to privacy which also makes it Illegal.
Like it or not, your son has rights too. Yes, your son is probably going to lie to you about things, but how the :swear: is he meant to trust you enough to be honest if you won't even begin to trust him?
I would suggest building a decent relationship with him so he feels that he can talk to you, instead of trying to control his life. before you get offended and start telling me that i shouldn't be telling you how to raise your kids, ask yourself if you *really* believe that your son can/will comfortably talk to you about his friendships, drugs (alcohol, cigarettes, narcotics etc), sex and anything else that he has to deal while growing up (when he gets into his teenage years, if he isn't already).
By trying to monitor everything your son does, he will only get better at hiding things from you. I believe the expression goes along the lines of the tighter you grip the more that slips through your fingers.