It is one thing to think about how many people will answer your call when you really need it, and another thing to think about whose call you will answer when they really need it too! Actually I have had a few friends that went through tough times and bad periods but for some reason they tend to keep to themselves rather than reaching out, which makes me feel like I haven't done enough to earn their trust.
Incidentally I have stopped celebrating birthdays for a while and it hasn't changed the relationship I have with my friends - I prefer to do something nice for them when the opportunity comes up rather than wait for an occasion once a year :D