The *NBC* has unified the operational Codes for all network providers as follows (MTN, Glo, Airtel etc now uses the same code:

*1. Account balance *310#*
*2. Recharge *311*pin#*
*3. Data plan *312#*
*4. Data balance *323#*
*5. Share Data *321#*

Note that, the old codes will soon stop working.
Like MTN checking balance with *556# is no longer available.