I was nodding my head in agreement up until that last bit. How is it more dangerous to pull off the interstate and park (assuming you are using an offramp and not just the shoulder) than making a phone call?
The most dangerous points in a normal freeway drive are merging and lane changes. To exit and park you do multiple lane changes off and on, merge, and have to navigate local traffic signals.
Compare to remaining in your lane, in smooth traffic, when you can see well ahead and know it remains smooth, while making a call and saying, "Just letting you know it looks like I'll get there around 8:20." "OK, drive safely." click (Any other variant of this conversation ends with, "I can't talk, I'm driving." click)
If I needed to make a longer call, of course I'd leave the road. But for this, I believe that just making it is safer.
I think GP probably was talking about using the shoulder. However, keep in mind that both merging on to the interstate, and city driving are significantly more dangerous than interstate driving. Combine that with the fact that calling to give an ETA is a lot less focus-consuming that most calls, and it is plausible that staying on the interstate is safer.
Stopping on the shoulder for such a trivial reason as giving an ETA is usually illegal and a bad idea anyways, so it shouldn't even be an option to be considered.
