Cisco Unified Communications Manager Express for Small Branch Office

[malonex3]

Hello. I will have a small branch of 3 to 4 offices where I need to provide VoIP phones. These phones will only be able to call between offices. They will not be able to call outside. I am considering recommending Cisco Unified Communications Manager Express. I am sure I will have more questions as this progresses, but to start here is what I would like to ask.

1. Is UCME the right path to recommend or is there a simpler way to provide this capability?
2. The documentation indicates a router is required, is that true or will a 9300 series switch provide the same function?
3. These phone will not have access to the Internet, how do I activate the Smart licenses?

[Leo Laohoo]

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@malonex3 wrote:
These phones will only be able to call between offices.

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How many phones in total? 
How are the sites linked together (dark fibre, internet, wireless, etc)?

[malonex3]

Total phones are unknown at this point but not expected to be more than six.
The offices are all in the same building and would connect via Ethernet cable through a switch.

[Leo Laohoo]

Cisco CUE/CUCM for six phones talking in an intercom (internal calls only) would be an overkill by lightyears.  

Asterisk in a Raspberry Pi could handle six handsets.