Nothing is fool proof, flaws can be found everywhere. No one can claim to have a vulnerability free security, one can find it, by one way or the other. Since mobile companies imposed balance inquiry charges, customers are very unhappy, but still people find there way out of these situations.
Codes for free balance inquiries of almost all networks were rumored here and there, some worked most of them not, and some got blocked. Here we got another one for you, try it out.
Telenor:
This is the time when telenor got caught in its own vulnerability, simply use **444## instead of *444# for balance inquiry.
Ufone
*333*1*2*1#
Zong
*100# and *310#
But as described earlier, companies block these kinds of codes, as they get notified.
But at the moment it is totally free to check your Telenor, Ufone and Zong balance, using these code.