I havenīt started commuting on my bike yet, but even when I did go by metro or bus to my other job, I just made the phone silent. Put on my minidisc or mp3 player and forget about everyone else.
I did the same when I had a car.
Unless one is on some kind of guard, or you own a business or something like that. I think any phone call can wait half an hour. If Iīm on a salary by the hours, I only take work related calls on work hours.
I used to freelance from home for about 3 years, and when I was at home before or after my "work hours" I just turned off my cell phone. Only very special clients had my home number. If someone wanted to reach me, they could allways do it at my house, or leave a message on the cell. The funny thing is, that I will turn on the phone and have a bunch of missed called (work related and others), but almost never got called home and rarely had any urgent messages.
So my point is, most of these urgent calls, at the end, are not that urgent.
Unless itīs going to cost you your job, just turn the phone off and enjoy the ride.