wELL NOw then
That being the case...he's a big boy now...with his big boy pants on.

Personally I do not go for vengeance as a norm...nor do I condone poor and irresponsible behaviour (disclaimer )
But if I were to condone poor and irresponsible behaviour...
If it were me...
someone whom I trusted ... thieving from my home....
that is a very violating experience...
and then walking around WITH such distinctive devices in front of you ...TRIES to sell it BACK to you!...and then says "he'll think about giving them back"!?!?!...ALL that is an absolute affront to a souls dignity, intelligence, and is basically either a consciously or unconsciously overt statement meant to goad you into seeing if you have enough testosterone to face him... and is begging for resolution.....

Here are 2 options...
A- honest...but boring...
or
B- the other far more fun .

A- beat the crap out of him until he apologized and gave them back...forgive him and help him out how you can afterward...proper "guy rules" (confront-fight-forgive-friend ) ...that is more honest...even if he is bigger and you have to clobber him from behind with a shovel in a dark alley at night it is more honest than option 2...but far far far less fun.

B- Much more fun..
Speaking of being violated...
the punishment should fit the crime...so...
I'd contemplate definitely not only hacking the phones ...
but as well ..
I'd sign him up to some very sexually ambiguous homosexual bondage and s+m dating and hookup websites and message boards as a submissive who likes it rough...and loves being talked real dirty to....
and if you know him well as well as you have mentioned...you could throw on the message boards his phone number ...email and his personal home address....then pull up a lawn chair out front and watch the fireworks show...
Very entertaining.
Hhehehe
(Big disclaimer! Being an intelligent, refined, cultured human being ...I have never myself done such a reprehensible and heinous act.... nor would I ever condone such base and primitive behaviour ...I just thought of it right now this moment and have never ever ever done anything similar.... )