I don't think there's a list available of which is the most recent version for each network... sadly lol
Are you in the UK? The bits about the shipping are relevent only to the UK lol
Assuming your warranty is intact, and there is an update available for your handset, yes, it should be updated for free, and yes, they do allow you to post them, though I'm not sure if that's all the Nokia Service Centres, or a select few - best to get in touch before sending it.
Also, you should send it Special Delivery so it's insurred, and ask about this first, but you'll probably have to pay for the costs of return too - so I'd pay for that to be special delivery too lol...
(Special Delivery items are insured for £500... which is nice in the event of them going missing... which does happen occasionally... believe me, after ebay, I know! haha

)
Nokia History: 3110, 5110, 7110, 7110, 3510i, 6210, 6310i, 5210, 6100, 6610, 7250, 7250i, 6650, 6230, 6230i, 6260, N70, N70, 5300, N95, N95, E71, E72
Current Phone: HTC Sensation - Android 2.3