iPhone / iTunes stop, restar, stop while on movement ....

Hi,

Since last week i have majors problems with my iPhone 5 32 Go under iOS 7.

It began with iTunes function, when walking across the street stop, start again, stop.. Once, it start it self. So i decided to restore iOS7, same problem and another while using GSM function. Problem occured while in movment. Material ?

I called Apple Care and received another iPhone, a refurb, i upgraded it from iOS 6 to 7, restored my backup and ... same problem. Software ?

After a second call to Apple Care the guy propose me to reset settings. So, with an iPhone under iOS 7, with my Apple ID as unique settings (mails, calendar & the only one track boughted on itunes), same point...

Since there no availability in a genious bar i'm expecting a second refurb. I don't know if it is hardware, two differents iPhone, software, a iPhone with only an apple ID & one track (music).

Another option is a bug on iOS 7.

Anyone ?

Nemrod