need to get a nano sim for my phone. currently have a micro sim.

will i be able to go into the store to do this or is it online

I think if you're an existing customer you may need to call them. If you call from a landline use the 0800 sales number from their site and follow the option for existing customers.

if want to make a call dial 0800 358 8460
they'll send you the right SIM for your phone when you take out your contract or upgrade them.

If you're using a device that you didn't get from them, you may not have the right sized SIM for your device to work. If you don't, you'll need to visit a 3Store to get the correct SIM or an adapter.

To talk to them about a phone SIM, call 333 free from a Three phone or 0843 373 3333 from any other phone*.
To talk to them about a Mobile Broadband SIM, call 500 free from a Three phone or 0843 373 0500 from any phone*.

*Calls cost 5p per minute from a BT landline, other networks may vary.

phoned 3 up and it will be in the post and coming in a few days time