I need to call an 800 # in the US, but cannot connect from mobile phone or by using a calling card. Can anyone recommend another method?

pop into one of those shops advertising overseas calls?

You can call 800 numbers IF they are set up to receive calls from overseas by calling AT&T USA Direct at 001 999 111 11. This is a free call so it doesn't hurt to try this option first.

I usually switch the 800 number to 880 or 888 and it works...

Switching 800 to 880 or 888 will not work unless the party you are calling has these numbers routed to the same phone. We had a major problem at our office a couple of years ago when another company obtained the same 7-digit number as our 800 number, but with the 888 prefix, and most fools would just dial us.

I did have the same problem a couple of years ago with my DTAC (post paid service), but DTAC has since fixed the problem, but they do warn you saying that you will be charged normal International rates, which is ok.

I am not sure who is your cell phone provider.

setup net2phone onto your pc, and dial your 800 numbers that way. last year, I had to contact my brokerage in the states via their 800 number. used net2phone to do that. you need to start your net2phone up with 25 bucks. that's the only thing I didn't like about it. ...but dialing 800 numbers is free.