AFAIK, it's not how BIG your bill is... it's how BIG your plan is. You could be paying through the nose, but if you're only on a 1000 peso plan, they won't offer much. That's why I switched up to the near-2000p plan. My bills used to be HUGE on the lower plan. Now they're fairly constant.

In other words, match your plan to your usage. Don't underestimate the value of free minutes.