Plan to go to the US in couple of months, does anyone know if I can use my phone (China Mobile) sim card
there? if not, how about any HK sim card work there? Thanks!

As long as your mobile phone is a tri-band or quad-band (able to to use the 850mhz or 1900mhz GSM bands). Of course you will be paying roaming charges on your HK/China sim card.

I used  my USA ATT phone in China which is a quad band phone.  A trid band will work too. ATT and T-Moblie uses GSM so does HK and China.  The phone needs to be unlocked too.

Back home in the USA my China Mobile sim card stopped working but it does work in HK, Macau and Taiwan.  This sim card is the older card that has no monthly service fee. These sim cards are no longer available for sale. It still works when I return back to China even after 1 year but I need to have money in the account. It's something like for each 100rmb it's good for 6 months.

On the other hand, I was told ( I don't know for sure ), the new China mobile sim cards will work in the USA.  

The newer sim cards requires a monthly service fee of 10 or 15 rmb. It is NOT worth using you China mobile account in the USA because of the outrageous fee. It's like using my ATT phone in China and paying something like 3 USD a min. In 20 mins it could be $60 for the call.

Edit for bad Sentence structure

[ Last edited by  Weelock at 24-9-2011 04:46 ]

Thanks for the info! I use a unlocked iphone 3g now using China Mobile (people) prepaid sim card, I'll be only making few calls in the USA, it should not cost too much, it is better than using the paid phones in the airport.

I suggest you purchase a triband dual sim card phone for use in the usa. Samsung, Philips, and LG have some good models for purchase in HK. Check to make sure both the sim 1 and sim 2 lines are are true triband. Some are triband only on sim 1.

Once you get to the usa, then you buy a pay-to-go sim card from either T-mobile/AT&T and place in the 2nd sim card slot to enjoy cheap local calls.

I think my Iphone 3g is quad band, so it should work in the USA, I check the Tmobile website, the cheapest prepaid card is US$25, it is good for 3 months, not cheap for only a few calls, but I check few carriers and T-Mobile is the best option. I might get one in Ebay before I leave for the US.

You check check out http://www.mycricket.com they have some pretty decent deals for prepaid cell phone plans.

i bought a PCC sim card in HK.
when i came back to the U.S., i was surprised to find that it still works.
(had to pay international roaming of course)