Should be many choices when the phone rings
Long ago I described how I want my cell phone to let me command it to play a recording to a caller noting that I have answered but need some time before I can talk, and also how I want the phone to stop ringing once I start fumbling for it. I learned that a few phones do have the former feature in a simple form, and it is something that is within the range of an app in some OSs but not others.
Let me expand those ideas to a more complete list of what a phone and voicemail system could and should do when a call is coming in. My friends Rohit Kare and Salim Ismail recently released a cool product they called Caller ID 2.0, which shows you more advanced screen pops on the incoming caller, such as their recent tweets and facebook status, which is quite cute if a bit spooky. But I refer instead to the choices I might make after seeing their number and other such information.
First of all, as before, I should be offered the ability to answer the call and play a couple of different recordings until I start speaking into the phone. As described, these recordings would be along the lines of, "I'm going to take your call but I am briefly busy, driving or in an audience. Please hold on while I get somewhere that we can talk." Since the phone should even know (based on rate of change of cell towers or GPS) that I am driving it should be able to figure out which of the two conditions I should report. While there are some minor privacy issues, it is worthwhile to let the other person know you are driving, as you really should have a different sort of conversation. This is so useful it would even be useful to let people know in the ringback that you are driving, but there are privacy issues on doing that, particularly with strangers, but even with spouses.
If the network will cooperate, it also makes sense to have choices that will, like the current "ignore" button, send the call to voice mail. These buttons however would control what sort of greeting is played, and perhaps other actions.
For example, you might send the call to a voice mail saying "Hi, I was too busy to take the call but I am with my phone, and I plan to get back to you within a few minutes. No need to leave a message." (Though if there was no caller ID, you might indicate that they should enter their phone number for the callback.) You could also have 2 buttons, to describe a longer wait time or different procedures, such as "I will call you back when I get to the office." As before, one button might make the greeting reveal things to the caller that you want to reveal, such as "Tell my location and speed." After all, quite often with a trusted caller, the main purpose of the call will be to ask where you are and when you are going to get where you're going.
Of course, as I proposed in 2005, if they do start leaving voice mail for you, and are on the same carrier, then an attempt to call them back should break into the voicemail session rather than giving you their voice mail.