Control Your Calls:
If you have a flat rate of calls, Control Your Calls is your application. It will be your best friend to save on mobile fee. It will help you not to exceed the limits of your rate, avoiding shocks when you receive the invoice.
Alternatively, My Call Duration:
If you have single plain plan of month like 300 call free then you can
a) go to "= Settings(Theme,plan etc.)" s page and enable your plan.
b) set your call quota i.e. 300 and
c) set your plan pulse rate like per minute or per second.
d)Then go to main screen (=Home), you will see one progress bar with text like 20/300.
e) now select 'today' drop down and select 'Day of Month' option and type your plan date. That's it. You will see your monthly data.
There's even some open-source app, Call Meter NG:
Call Meter lets you keep an eye on your mobile plans.
It shows statistics of your calls/sms/txt/data traffic and lets you set limits for each of these plans.
Call Meter supports a huge amount of billing modes to let you adapt it's behaviour to your operators billing.