Does the 2851 need an additional module to make it work, also what would i use if i needed to install more than 240 phones? this is the maximum amount of phones that the CCME supports.

Depending on budget and if you have more than 240 users you could do a couple of things that come to mind immediately:

1. Unified Communications Manager Business Edition with the 2851 router that contains multiple VWIC-1MFT and/or VWIC-2MFT modules and a complimenting suite of DSP (PVDM) modules to handle both the data requirements and isdn voice requirements. This solution supports both the voice and voicemail requirements. You can add VT advantage to this system to allow peer to peer video conferencing but short of that, I think you need another system to handle that piece.

2. Multiple CCME routers dividing the users to keep the user limit under requirements. If you want voicemail, you will need to look into Unity Express and purchase that module as well. You will need to define how many concurrent VM connections you want to allow. As above, you can add VT advantage to this system to allow peer to peer video conferencing but short of that, I think you need another system to handle that piece.

Hope this helps...

dford is right as for the mentioned installation size CCM is a better choice than CME.

Couple of precisations:

- 7815 is kind of oldish. On a budget, look for the 7816 that is entry-point for rack-mount.

- CME does support extension mobility in lates version 4.2

as for preferences I wouldnt use EM with CME, but as for your budjet thats another choice.

and that is correct EM is supported on CME

Prerequisites

?Cisco Unified CME 4.2 or a later version.

Restrictions

?Extension mobility on remote Cisco Unified CME routers is not supported; a phone user can log into any local Cisco Unified IP phone only.

but not for remote users. also you want video conferencing, and If you are well versed in CME than yes you should otherwise, for time and convience, use a callmanager 4 7815 - 7825.

you will not have any restrictions preforming what you need to do. you just need to know how to do it.