In response to a comment and to clear up whatever confusion there is over terms for the "third sex", these are generally accepted definitions.
1. Cross-dressers - These are men that like to use female clothing and experience what it feels like to be the opposite sex. They, however, do not want to change their sex nor will they surgically alter their body and in general are seldom seen in public.
2. Transvestites - Sometimes defined as "serious" cross-dressers who go to greater lengths to look feminine. e.g. with elaborate make-up, wigs, breast pads etc.
3. Transsexuals or Shemales (or ladyboys in the ASEAN context) - Dead serious about changing sex - they grow long hair, take hormones, do surgery as soon as they can afford it, they go all the way in dressing and on many occasions look better than genetic girls. Before the actual sex change operation known as pre-op shemales and after as post-op shemales.
In the Singapore scene, sex change (Male to Female) was done at Alexandria Hospital by a Prof. Ratnam. Those that went through the operation, sexual reassignment surgery or SRS, were allowed to change their sex in their identity cards to female and could get married. However, after the professor passed away no more operations were performed. This was also due to the excellent value offered by Thailand which is now rated as number one in the world for sex change operations. Singapore still recognises transsexuals that undergo sex change operations as being female.
Strangely enough, Thailand doesn't and the ladyboys or katoeys as they're called there are still legally men.
As far as NS or National Service in Singapore the general principal is that men who tend to be effeminate (and haven't gone for the op) are usually channelled to clerical posts. Incidentally in Thailand, men who are clearly ladyboys are excused.
I hope that clears things up.