Service menu

Samsung

*#*#197328640#*#*
*#0011#
#2683662# (service menu on Samsung Galaxy, but doesn't work on every model)

Sony

*#*#*386#*#*
*#*#*585*0000#*#*

iPhone

*3001#12345#*

HTC

*#*#7262626#*#*

Mediatek

**#*#3646633#*#***
MTK Engineering Mode

OnePlus One

Service Menu – *#0*#