* REGISTER transactions:
  Currently siproxd does only support *one* Contact header in REGISTER
  transactions. If an UA does send multiple (which is legal) funny things
  may happen.
  There are one or two funnies associated with REGISTER transactions that
  should be mentioned:
  1)	There can be multiple Contact URIs in the request.  It is legal
 	(although very rare) to register multiple extensions at the same
	time.
 	When multiple extensions need to be registered, they are generally
 	registered separately.	You probably don't need to worry about this
 	for the time being, but it is probably worth bearing it in mind.
  2)	There can be multiple Contact URIs in the response.  If more than
	one UA has registered for the same AOR, then the response to the
	REGISTER will contain all the registered AORs and their current
        expiry times.
 	None or some of these may need 'unmapping'.  Again, this probably
 	isn't something you will come across that often, but knowing it can
 	happen may save you some debugging time later.
  3)	The Contact in the request may contain '*'.  This is used by some
 	phones to deregister all registrations for the specified AOR.
  4)	Sometimes, there is no Contact in the request.  This happens when
 	a UA is querying the registration database.  This is sometimes used
 	for diagnostic purposes, although I suppose a phone could do this
 	automatically for some reason.
  5)	The definitive expires time is not found in the request.  This is
 	simply a suggested value.  The actual value is in the response from
 	the registrar.
  For the definitive description -> RFC3261 section 10.