i'm looking on some information to start upgrading to voip phones. i'll have about 10 phones to begin with, all at one location but distributed is in the near future. i have a 2821 router that the company had baught before i came on. what other things do i need to be looking at and what version software do i need? does the software scale with size or do i just get the latest? anything will help even pointing me in the right direction for some reading material. all is welcome.