I’m proud to say I’ve been doing this since I got my iPhone. My bank, doctor, dentist, auto insurance, roadside assistance, and others are all in there. A few tips:

• I have to call one number to discuss my checking and savings accounts with my bank, and another number to talk credit card. You can enter more than one number for each company, and you can customize their labels (“credit card” rather than “work” or “home”, for instance).
• If the business in question is local (e.g. doctor) add the physical address also. It’ll make googlemapping easier.
• Some (smaller) businesses’ websites will have odd or rather long URLs. Rather than putting them in your bookmarks (or in addition to it) add them to their entries in Address Book.
• I also created a Smart Group called “Biz” with the rule being, Company is set, Name is not set. This gives me a quicker way to access those “impersonal” companies.
• This is relatively unrelated, but consider adding the Poison Control Center to your contacts (1-800-222-1222)

Why not have all those customer service numbers in one publicly-available repository? Maybe have people contribute voicemail shortcuts for each system (“To talk to a human, press 6, 6, 5, 9, 1, 8 and then cough loudly”).

To whoever does this and makes a zillion bucks on AdSense, you’re welcome.

Just to add… I’ve been totally digging 37signals’ Highrise app. One of the things that constantly impresses me about their apps, including Highrise, is how simple it is to use for the average joe, but also how powerful it can be for a full fledged business.

If you haven’t heard, Highrise is they’re answer to bloated ‘Customer Relationship Management’ software but they sum it up best: “Highrise helps you remember who you talk to, what was said, what to do next, who to call back, when to follow up, and more.”

I used it extensively for keeping track of a recent battle with Verizon in which every time we called they couldn’t pull up any records of our previous discussions… wanted to tell them to get Highrise!

http://highrisehq.com/

No number is more important to have handy than your ISP’s tech support line when you’re stuck without internet. I’m never reminded how dependent I am on online services as I am when I can’t get online.

Address Book is a great place for that sort of info esp. with an iPhone. I found myself doing the very same thing last week. Etrade, the Oil Change place and the deli around the corner. On a related note, there was a great post on the Cranking Widgets blog about the numbers everyone should have in their phone. It's a great list and it helps ease the mind of recent parents (or those who are about to be) with numbers you don't want to look for in a panic.

I’ve had great success using iCal to track customer conversations. I create a new event for each conversation, title it with the company name and keep notes. A search in iCal’s search field quickly yields an entire history of conversations by date and the appropriate info.

As a network engineer, I have to call ISPs/Telcos quite often. Things seem to go down when I’m not at my desk where I can open up the spreadsheet with circuit IDs and who is the provider for whatever location is having the problem. Now I have all of that info in the notes field of the contact (each location) so I can look it up on my phone to give tech support.

Great tip! That the A-Z organization is super general hit me a while ago. It was kicked off by this article by Laura Stack (interview post coming up this week): Build an effective time-management system. In addition to keeping agendas here (with an optional index in the front), she lists these things:

Also, keep track of lists filed behind the letter of the category, such as goals, values, classes to attend, books to read, shopping, errands, gifts, chores, vacation ideas, purchases, birthdays, holidays, and special occasions.

GTD-ers will recognize checklists here.

More here, if you’re interested: Your portable A-Z section - not just for contacts.

The most important number to have is the number for roadside assistance from your auto club or insurance company. I know I’ll lock my keys in my car sometime and my roadside assistance card isn’t going to help me from the glove box. I just hope I don’t lock the cell phone in too.

why isn't there a central repository like wiki where all numbers are stored

I can’t tell you how many times having FF#’s and Library Card account numbers on my phone/iPod/Plaxo/.Mac/GMail/ accounts has kept me from getting seriously annoyed.

I agree with the above comments on the necessity to create a dedicated group of contacts in Address Book for your Cust Service .

After investigating the same issue 6 months ago, the solution I landed is a mix of two Mac applications (since you can’t get rid of your laptop :-)) : SoHo Notes and Daylite.

They both seamlessly integrate with OSX’s AddressBook and iCal modules, and are IMHO the best - respectively - Notes/Password manager (which you can link to contacts) and Contact Management package.

Give it try, since they’re more than affordable. Hope it helps,