Some may or may not work as I have not personally verified each.
On your iPhone’s Phone App dialer enter and press call:
Field Test Mode: *3001#12345#*
General Test Mode: *#0*#
Display IMEI: *#06#
Call Forwarding: *#67#
Detailed Call Forwarding: *#61#
Available Minutes: *646#
Bill Balance: *225#
Hide Caller ID: #31#
Show Caller ID: *31#
Billing Cycle information: *3282#
SMS Message Center: *5005*7672#
Activate Call Waiting: *43#
Tech Insight 