Want to buy reliable used mobile phone

Can anyone suggest a secondhand shop in Prague where I can buy a reliable mobile phone?

Thanks.

 

There is one shop with used phones in Muzeum metro station. There is another one in Vodickova (cca middle of Wenceslaw sq.) by Svetozor.

 

I also remember one being opposite Narodni trida metro station, a little way up on the other side.