Thanks for the replies.
I don't actually own this phone but am I'm seriously thinking of getting one in the next few weeks and this is a serious issue for me.
I'm in the UK, so it's the Galaxy Portal that the i5700 is sold as.
The methods described by
Andronix: "only if it was set to silent prior rebooting" and
: "Mine is always set on vibrate, so that's what it does when it boots".
did NOT work on the model on that I tested in the T-Mobile shop (who supply it with Android 1.5).
BUT, they did work on the model in the 3 Mobile shop, which was running Android 2.1.
Any comment on this? - I assume your i5700s are running v2.1...