maybe don't use cards for all aspects
If you are going to need to have a typed list at end of the week that you can attach to something like a report or a time sheet, you can save writing time by using a pda or computer. Palm can be used in handheld or desk top and you can print out any aspect of it you want. Palm can let you sort as you go. Cards you will have to sort and rewrite from. You can set up memo categories and move items so quickly from one to another or from top to bottom (it sorts a-z and by number).
I love to have the bird's eye view and tried to use cards. I like cards for recuring "maintenance" tasks. I like to rotate them through a tickler file byu date. I also like cards for making a list of projects, one per card. Esp. helpful if it is a project with many parts and I need to move the moving parts around. I had a system where errands were listed on orange cards, calls on blue, writing on green, but I found I had to do a lot of re-writing and referencing of data so I gradually gave it up.
Let's say you have 50 calls to return and you need to keep track of status and outcome and report it to someone at end of week, cards may drive you nuts. In contrast, you can move info readily between Palm categories such as "call-day time", "call-nite time", "waiting for...(response of some type)", "wants literature sent by mail","wants to be e-mail only", or whatever you want. On the Palm desk top you can easily use a date-time stamp (I can't get this to work on hand held) and that comes in handy.