Hosted IP telephony

Hi, We are an Internet and IP telephony provider in Canada and looking for options to reduce our costs. We are exploring hosted IP telephony option to see how it can help us reducing cost and operational headaches. We have few hundred of phone adapters to register and this number increases from day to day. If you provide this type of solutions or know providers of this type of solutions please contact me. Your help will be appreciated. Thank you Karim