Hmm. This sounds extremely sketchy. The first thing I do with my android devices phone is root them and install a 3rd party build, usually LineageOS ( http://lineageos.org ) That protects me from at least some kinds of Carrier Fuckery, like Carrier IQ ( http://mashable.com/2011/12/01/carrier-iq/#hc ) and OEM fuckery, ( http://www.techradar.com/news/beware-these-android-phones-sent-texts-other-sensitive-info-to-a-server-in-china ) . Of course, Apple users are not immune either ( http://bgr.com/2011/04/20/apple-recording-storing-gps-position-of-iphone-3g-ipad-users-video/ ).
This does not of course protect me from network analysis or spying on the data streams coming in and out of my phone, and the Radio software is a hot mess of proprietary code and horrid security practices. But at least I can push back a little bit. Rooting the device also means that I have complete control over what is on it -- I am territorial about my bits.
I have trouble imagining that anyone would lease me a phone and allow me to hack it in this way. Buying used or reconditioned gear seems like a much more sensible course of action.