I first modified my penis at the age of 35 when I had it pierced (reverse Prince Alfred) and some three years later I did a subincision myself, opening the urethra for half it's length (in my case a little over 3.5").
The subincision was made so that my penis that had an opening akin to a vagina. I am bisexual and identified with the modified penis as being part penis and part vagina, just like my sexual identity - neither fully heterosexual nor homosexual.
In addition to the cosmetic variance it also allows my partner to insert a finger down my urethra for sexual stimulus - this is very arousing and prolonged manipulation in this fashion produces a quick and strong ejaculation.
