Aside from the obvious security dealings, and maintaining absolute control of your information, I question the reasoning of handing your old phone in to get a new one.
I see no benefit from this, and if I can make use of the device for other things, I keep it.
You can also donate used handsets to charitable organizations, like abused/battered women, so they have instant access to 911 if their spouse has a history of abusing them, for this, I find the reason to keep my old phone, a matter of importance. I get no benefit from giving my phone to a carrier that will simply toss it in a bin with all the others, for recycling, and probably make more money off of you when you sign up for another subsidized phone. But no matter what you do with your phone, always wipe the device clean of all information, regardless if you think it might be irrelevant, to a thief, nothing is irrelevant.
I never keep an SD card installed in a device I am giving away or donating, just for this single issue....lost data.
Some people store their social security card numbers on these, and use them as passwords, if they find the last four digits, it does not take long to come up with the first string of six to get the complete number, and the state of issue.
What we all take for granted, thieves do not, every scrap of information has use to them, it is a paper trail of sorts.
