I have a land line telephone number and because of having cell phones I would like to cancel the account and stop paying the monthly charges.  Anyone know how to do this?  Thanks in advance.

You tell your provider that you cancel the contract, then the provider will probably do this to the next possible date

Last month I just cancelled 2 land line numbers with TOT, which I have had for many years.The numbers were in my deceased wife's name.I went to the local TOT Service Center, so in order to cancel they needed copies 

of my passport, copy of mariage licence, copy of wife's death certificate and I also gave them copy of house certificates, the so called Tabian Baan.Then they will settle the accounts up to the date of cancellation.My last bill will arrive in February, and then the numbers are cancelled.Very easy it took less then 20 minutes.

For me went to True office, about 10 years ago, just must remember the cancellation [doing it at TRUE] last for 6 months, so have to return to True Office every 6 months to sign the cancellation form. [only forgot once soon see when the 107 baht TOT bill arrives] 

Just don't forget, if you have ADSL/VDSL internet service, you still need that line.