best practice in archiving CDR data

I am using Postgres to store CDR data for voip switches.  The data size quickly goes about a few TBs.  

What I would like to do is to be able to regularly archive the oldest data so only the most recent 6 months of data is available.  

All those old data will be stored in a format that can be retrieved back either into DB table or flat files.

Does anyone know how should I go about doing that?  Is there any existing tool that can already do that?

thanks,

jb