There is no non-expiring card.  Virgin Mobile USA has CDMA prepaid phones
with a ninety day recharge cycle and a two month grace period between top
ups.  Virgin mobile can take a credit card to do the topup automatically
when you are out of the country.  I'm not sure whether they will take UK
credit cards or not, but you can buy prepaid Mastercards and any Riteaid
drug store in the US, top it up and let it auto recharge your Virgin.
Remember, the minutes roll over.  I'm not sure whether you could take four
topup cards back with you to do topups manually from there.Usually, there is
some backdoor number which can be called for that purpose.

Tracphone has a prepaid card that goes a year at a time, but Tracphone has a
very bad reputation for other reasons.  Both of these solutions require you
to purchase a non-GSM phone.

If you've a got a friend with ATT in the US, they have a special running
right now which would let your friend add a second line pulling from his/her
minutes at US$10 a month.

T-Mobile had prepaid card that were good for a year on a special basis, but
they are gone.  You can still find some people hawking them on e-bay.

Stu

Actually T-Mobile US now has prepaid sim cards.
Expire?  That you will have to ask the dealer that you get it from.

TMOBILE has the 1 year No Expire promotion running again. If you top off a
current TMOBILE EasySpeak prePaid acct with $25 or more of airtime, it will
not expire for 1 year. Top Off of the $25 must occur before June 30. Details
at http://kickme.too.wirelessworld
You can find activated TMOBILE Easy Speak SIMS with about $50 of airtime for
about $25-$30. then you just need to add the $25. If you go to a TMO store,
their SIm Starter kit is $50 with SIM and 120 minutes airtime good for 60
days.
Last but not least, being in the UK, www.expansys.com now sells TMOBILE
PrePaid SIM kits for $50 us dollars

For GSM with SIM cards it does not exist.  You can get prepaid, but
you will require another handset.  Often you can get used handsets
that will work.  There's a service called Justalk where you can get
service for $8.49 (for 40 minutes) with the service good for 180 days
before you'll lose any credits and the service will be disconnected.
It requires that you get a handset that was on the AT&T (TDMA)
service.

http://www.phoneshark.com/showwirelesscard.cfm?f=11&t=11&p=8314#phones

With this service you are often given service with a number that is
not local to you, but each account is given a toll-free (freephone)
number so that your callers don't incur any extra charges.

If you go to the above offer and buy the refill all you need to do is
call Justalk customer service and tell them that you wish to initiate
new service.  They'll ask for the ESN (electronic serial number) that
you'll find on the handset under the battery.  They'll then apply the
credit to your account (the so called "PIN" a ten-digit number.)
They'll instruct you how to program your phone with your phone number.
You can always buy another PIN over the net and input the PIN to get
an extension of the time on your account.  The number to add airtime
is a US 1-866 "freephone" number.  If you're unable to call US
freephone numbers you could have a colleage in the US call the
recharge number and input the time for you.  It would end up costing
you USD17 per year for service.  Or, in the alternative, if having the
same number is unimportant to you you could just let the account
expire and get a new account the next time you are in the US.  If you
had any money on the old account you would however lose whatever
credit you had.  The only thing that's really inconvenient for you is
that you would be required to get a compatible phone as the phones
that justalk uses are not GSM and thus not SIM compatible.

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          remove NONO from .NONOcom to reply

Some alternatives to prepaid if you visit the USA frequently.  These options
maybe more expensive than prepaid.

With AT&T wireless, you can put your phone under 'suspension' when away.  So
you could get and AT&T monthly account then 'suspend' it when you're not in
USA.  I don't use AT&T but a friend who does told me about it.  He travels
out of USA about 6 months per year and when he leaves he suspends his mobile
phone.  You have to get the details from AT&T.

You also could get a Cingular monthly account with rollover minutes. When
you're not in USA, the minutes would rollover and accumulate so when you
return to USA, you'll have lots of minutes to call your friends, relatives
and business associates.