For those who want to go to Singapore, sometimes it is required by an immigration official to present an invitation letter from a relative or friend who is in Singapore. Last time, when I went here, I only have an invitation from my sister which was just a simple invitation letter with her name and IC number.
What I heard from my friends, right now they require an invitation letter signed by officials from the Philippine Embassy here in Singapore. This invitation letter should be applied personally in the embassy and has a fee($45?). My housemate went there last Wednesday and he was in for a surprise. The invitation letter will be processed for several days and you would only be able to get a copy after that time. Not recommended for those who procrastinate. If you have friends or relatives who plans to visit you, try to get an invitation letter as soon as possible.