If you have own the Nepal Telecom Landline/PSTN number, then you can check the bill of that number by just sending SMS.
Send SMS to 1415 by typing CB*landline number(remove the first zero of the area code). Example: type CB*14156435 and send to 1415. You will get the message instantly with details like due amount and credit balance.
You can use the NTC website and check the bill amount online but for this you need the special a/c number which can be found in the bill which we get from NTC office during payment.
So just sending SMS would be great to check the landline bill amount from Nepal Telecom mobile SIM card.
Using IVR (Interactive Voice Response):
You can easily check PSTN landline bills via PSTN bill enquiry system. Dial 1606 from your PSTN landline. Press 1 or 2 for language you are convenient with. Press 1 to know your landline bill. Then, press 1 to know your monthly bill or 2 to know your bill till date.