Exchange 2010 migration from 2003 - Office Communicator 2007 R2 considerations?

Not sure if this is the correct area to ask, but given this is where migrations are generally discussed I thought it was worth a shot.

Currently running Exchange 2003 and moving to Exchange 2010 (no need for help there), but in this case there is Office Communicator 2007 R2 in place.  Does anyone know of any good documentation about how this works during the following:

1. In co-existence when 2010 is installed, does this affect communicator?  Or can you safely install 2010 alongside 2003 in co-existence and 2007 R2 requires no configuration straight away?
2. When mailboxes move across to 2010, how does this affect communictor?
3. When 2003 is finally turned off, how does this affect communictator?  Do you need to reconfigure it?

I have very limited exposure to communicator, so would like to do all the research well before needing to do anything!  Thanks.