How long would it take O2 to switch my regular sim over to a micro sim?

Don't quote me but I am sure when I switch sims on o2. It was the next day, the 'old' sim stopped working, I swapped to the new micro sim and it was working.

I just upgraded to a new phone on O2 which used a micro sim and it took less than an hour for my number to transfer from my old sim to the new one.

Yeah, usually within an hour but O2 say to allow up to 24 hours.

When I switched from iphone 3gs to 4 (needed to switch sim to microsim) the person in the O2 made the switch instantly

Not sure about O2 but Vodafone took about 10 minutes.

Why do some phones use a micro sim and most others use a normal sim card. Is there a reason for this.
When I changed sims 2 years ago to a 3g sim. Im sure It tane less than 5 hours for 02 to transfer my number over.

Darren

About 30 second when done using this link.

http://swapmysim.o2.co.uk/

I had to do mine when I got my Iphone 4s, took about 30 seconds.

Micro SIMs take up less room so it allows you to make a smaller device, that's the only real reason.

Function wise they are identical as all you are doing is cutting away the excess space from a standard SIM (Mini SIM)