NO NO NO NO NO NOOOOOOOOOOOOOOO
It's partly the issue of multitasking - when I call during the work day, or at night for a work-related thing, it's fine for the other person to be working. But when I call at night, please back away from your keyboard and turn off the tv. Talk to me. Focus on me. (yes, it's all about me!) I'll do the same for you. Now I get to compete with your personal routines? NO THANKS.
My time in the shower or bath is relaxing time. It's "me" time. It's not "oh, could you hold, I have to rinse my conditioner" time, or "wait a sec, I have to wash my [insert body part]" time. Yes, I realize that this opens up many possibilities for those who enjoy phone sex, but for me? NO THANKS.