By the way in answer to the OP it is routine for some people I ride with to have 3 or 4 pints. I don't know how they do it myself, if I have more than half a pint (over any stretch of time) and cycle I feel very dehydrated indeed. So it's not something I do.
On the risks side I think you have to bear in mind the route, distance and how much you've had to drink. I think from what I've encountered in other people once you get into 10+ units territory you're asking for trouble. I had a friend borrow my bike and cycle back from a neighbouring town on cycle paths on 6+ pints. I'm very glad he didn't go on the roads. One also has to bear in mind say the risk of assault waiting for a taxi or walking home which are fair risks. Walking home is not without its risk either, thousands of people end up injured or hospitalised doing just that. I think overall if you are going to get drunk cycling is one of the better options, not the safest (far from the most dangerous) but not far off and pretty practical. The safest is to drink as little as possible and have fun.
I don't think cycling whilst on the phone is a good idea. Then again, in the same vein it's not illegal and you can't go round equating that to driving round a large metal box with perhaps a hundred times the KE.