If you have the basic version of "The Sims", your phone directory can only hold 9 family names plus "Services". This isn't a problem, as you can only have 10 families in a neighbourhood. When you install "Hot Date" and/or "Vacation"/"On Holiday", your phone gets upgraded so that it can hold 12 entries (10 family names plus "Services" and "Call cab").
When you go into the Downtown or Vacation Island areas of the game, you meet computer-generated NPC Sims. If these Sims are Downtown, they will be called Something Townie. Still not a problem, as your phone holds 10 family names. However, as soon as you go into Vacation Island, you start meeting families with different surnames (named after science fiction & fantasy authors!). And then you hit a problem, because your phone directory only holds 12 entries. You can make friends with people, and then not be able to find them again to invite them over. How awful!
Anyway, today I read the "Hot Date Gameplay FAQ". It says:
Q: I have more than 12 Townie friends but I can't find them in the phone to call them. Where are they?
A: The phone can only hold 12 names in a pie menu, so just hit the TAB key when looking through the Townie names to get to the next 12 names in another pie menu.
So this is the solution to my problem! As I'd never bothered making friends with Townies, I hadn't noticed that you could do this. And the game had been driving me nuts for a whole week before I found out - grrr! I've emailed EA and asked them to add this question/problem to the"Vacation"/"On Holiday" Gameplay FAQ, but I thought in the meantime I would post this on livejournal so that everyone I know who plays "The Sims" can find it.