I am trying to look for information that can tell me the
difference between the two in terms of ease-of-maintain,
ease-of-implement, and scalability. If you have such kind of
information, would you please share with me?
Apples and Oranges. OpenSER is more of a proxy/router and FreeSWITCH
is... well.... a switch. OpenSER is definitely better at dealing with
broken devices (i.e. most linksys phones/ATAs on the market) behind
nat. You might consider using OpenSER as a registrar/proxy and using
FreeSWITCH to do the call accounting and routing to/from carriers.