Air carrier exiting runway at LAS experienced potential taxi conflict; failed to contact Ground Control; changing directly to ramp control; in contrast to ATC direction.

Narrative

We recently received a briefing directing a change to the Ground/Ramp radio contact procedures at LAS. As I understood the briefing; I; as the pilot monitoring; was to have Ground in the #2 radio monitoring the Ground frequency; and have Ramp in the #1 and contact them directly prior to entering the ramp. during this event; I had the radios set up as directed by the briefing and the instructions printed on the weather packet. As we exited the runway; Tower instructed us to contact Ground. Having just reviewed the 'new procedure;' I elected to continue monitoring Ground and call Ramp. I assumed that Tower just said contact Ground out of habit; as there was no immediate conflict on either taxiway. Crossing Taxiway C; I called Ramp who told us to turn right on Taxiway C to B4; and then changed his mind and said call Ground because an RJ was joining Taxiway C westbound at Taxiway C6. I hesitated to respond and he then told us to turn left through Taxiway B5 and right on Taxiway B and the gate. Once at the gate; the Captain and I discussed the event and decided to call the Tower. The Tower told him that they want us to contact Ground and then Ramp in all situations. The ATIS also has a message alluding to the fact that their intention is for everyone to contact Ground and NOT simply monitor on the #2 radio. I realize that in the first event that I did not follow the instructions given by Tower and that doing so would have prevented all the confusion in the instance. However; I was simply following the ridiculous procedures dreamed up to make what should be a very simple exercise of exiting the runway and taxiing to the gate a total disaster.