Hi
You can use a 3825 in a few ways:
SRST - configure it as SRST to enable phones to register to it in case your CM server fails. This will get you basic telephony, simple config, and up to 336 phones.
See this URL : http://www.cisco.com/en/US/products/sw/voicesw/ps2169/products_configuration_guide_book09186a0080667143.html
CME-as-SRST - you can configure SRST in a more CME-like way in order to get better feature support in failover mode. I believe this supports a max of 240 phones however.
See this URL:
http://www.cisco.com/en/US/products/sw/voicesw/ps4625/products_configuration_guide_chapter09186a00807e0566.html
Regards
Aaron
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Aaron
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