Yes, you will probably have to phone up Telstra to activate global roaming.
They will tell you if there are any charges involved.

The actual call costs will depends on the network they use for roaming.
Obviously it will be more expensive than here in Australia. Pre-paid may be
cheaper but its not convenient for everyone, especially if you need to be
available at any time on your normal number.

Best bet is to ring Mobilenet on 125111 and talk to them, they have a
section for International Roaming they can transfer you to, they can quote
you prices for calls on the network over seas and instructions on how to
manually select a network if needed, you can still pick up a prepaid card
over seas, theres no charges on your mobilenet service unless you use it
(both inbound and outbound are charged) just be aware they US sims apart
from the new Tmobile service you have to get directly off tmobile are locked
to there region you activate it within.

Most likely you would need to call Telstra to have International Roaming
activated

Yes

Prices based on overseas rates. Look at www.telstra.com/mobile

Quite often it is

I use the 6310i quite often in USA.

Firstly, as stated here by others, you should arrange International Roaming
with Telstra.

WARNING.  Do NOT try to use your hand set in the immigration & customs hall
at LAX - the paranoids will confiscate the 'phone.

Outside, just turn on & you should pick up either Cingular or AT&T Wireless
within a few minutes - sometimes you have to do a manual network search.

I would advise that you select Cingular (if not selected by the auto search
do this manually) - I believe that they are cheaper than AT&T (but have just
made a takeover of them); apart from that Cingular have correct
implementation of sms, which AT&T have never bothered to do.

Outside California you should also be able to get T Mobile, who simply
piggyback on Cingular in California;  their own infrastructure elsewhere.

For rates and further info see http://tinyurl.com/3dfys

Don't forget to take a car cigarette lighter charger, or your plug in
charger, with a power point plug that will allow the Australian prongs to
piggyback into the USA power system (Electronic Dick sells them). If you
have the regular Nokia charger make sure it is dual voltage as well.

Good Luck!

Check with Telstra 125111 to ensure your account is enabled for roaming.  If
you have had a Telstra post-paid account for more than a  year, chances are
that it is already enabled.  Telstra automatically enables roaming on most
post-paid accounts after about 6 months, assuming your payment history is
OK - but wise to check that you're enabled.

Roaming is not available on prepaid accounts.

Call prices are in general high - roaming is convenient but it sure costs.
Plan in terms of well over A$1/min for calls to US numbers while in the US,
closer to A$2/min to call Australia while in the US.

For incoming calls, you will pay about $1.40/min.  Ouch.

A far better option:  Purchase a prepaid card while in the US.  The Virgin
Mobile deal in the US, see www.virginmobile.com, is hard to beat.  Virgin
has roaming deals nationally, a somewhat rare accomplishment in the US
mobile phone scene.  Call costs are far more reasonable than the roaming
costs quoted above.

On the technical side, the 6310i will work fine in the States.  Make sure
that your power adaptor will handle 110 volts anf that you have a US <=>
Aussie powerpoint adaptor.