Hi there. There is one that shows a pop-up to alert you when someone is calling, it just comes up on your screen, but I can't for the life of me think what it is called. I remember you had to pay a small fee for it too but it wasn't that much.
Also consider if you have a mobile phone, you can 'Divert' your calls to your landline to another number(your mobile) and this would come in handy for that. Simply answer the moby, see who it is and call them back.
Brl.