If you do purchase several options, see if you can get a discount. Allows you to identify the caller before you pick up the phone. Must purchase a separate display component or a Caller ID phone. Useful if you get a lot of calls and you don't want to miss any. Of course, you should evaluate how important those calls are anyway.
Most phone calls can become time wasters.
Select Combines Call Display and Call Waiting. This is supposedly free if you subscribe to both, but really, you've already paid for both of those options if you subscribe to Call Display and Call Waiting. If your phone is always busy, you could try Call Waiting which is cheaper. Paying a monthly fee will cost you more in the end than purchasing your own answering machine if you're away. Most modern answering machines will allow you to retrieve your messages remotely.