I need to setup two sites each having a UC520 system that need site-to-site calling via extension number. I have never done this before so I don't know what to expect. The sites are already interconnect via a QoS enabled VPN.
The one thing I do know I have to figure out is how many digits to use for the extensions. Should I use 3 digit extensions and use the first digit to identify the office? Example would be Site A extensions would be 201, 202 and so on and site B extension would be 301, 302 and so on. Or should I use 4 digit extensions like 2201, 2202 for site A and 3201, 3202 for site B. What are the pros and cons of each? There isn't going to be any more than two sites in the foreseable future.
Also feel free to give pointers for anything else that I need to be aware of with this enviroment. All input would be greatly appreciated.