LAN Admin Responsibilites

I work for a company now with 3 offices and around 300 total users. I have LAN and phone responsibilites. Right now the Phones are taking sooo much more of my time then I think it should. I would like to know how much of your time do you spend working on the phone system, specifically the bills? What do you do with them? I have to aduit each bill, dispute charges,do histroy reports and so on. Should accts payable do some of this work?

Thanks