Mobile phone sim cards in the US

[DanS]

Can somebody explain to me how these work in the US?

Right now in the US market, you buy your phone from your mobile provider. For instance, I bought my phone from Virgin Mobile and have a pretty cheap pre-paid plan (~$6.75 a month). But they have a pretty limited phone selection.

The iPhone to come out next year is said to be unlocked, so I was wondering about the details on sim cards in the US and what networks they hook into.

[Pekka]

Well, all the GSM networks at least?

[Pekka]

What the unlocked means you can change your provider. That's all. That is, you can use that phone (that is unlocked), and change any working SIM to it and basically change the provider. Within the same phone.

[DanS]

GSM may not be the same in the US.

Anyway, in Europe, do you keep your phone number if you switch providers?

[Pekka]

We do. These days we also keep the prefix that was used to identify the provider.

What do you mean GSM is different? It's a standard. Now, it operates in different band in the US... in Europe it's 900 MHz or 1800 MHz.. in US it should be 850 MHz and 1900 MHz, because the earlier ones were already taken and busy!

[Fake Boris]

DanS may be right, IIUC some of the North American carriers actually provide no way to change the SIM on a phone.

[Dinner]

There are several different types of networks in the US. The "old" cellphone (meaning nondigital) networks (which are normally the cheapest), the GSM (EU standard) system, and those based on Qualcomm's CDMA technology. GSM is the only one which uses the simm chip under the battery as far as I know.

You can switch the simm chip easily by removing the battery and popping the chip out of the plug located behind the battery. Put the new chip in and you are ready to go. Normally your phone numbers are stored in the chip so if you change chips you lose you phone list (though some new models don't work this way).

[Dinner]

Then of course there are hybred networks which use cell and CDMA or cell and GSM (one for data and one for calls or for back up range on reception, etc). The technology and combinations can get complicated very quickly so a lot depends on what system you are using.

Having a phone "unlocked" means you can shop around to other carriers. For instance many "world band phones" can work on both GSM and CDMA but not all GSM or CDMA phones use the same frequencies because different countries specify different frequencies. Unlocking the phone let's you use other network carriers on that phone instead of just the one who originally sold you the phone.

[Dinner]

Originally posted by Pekka

What do you mean GSM is different?

GSM is indeed a standard which let's electronics manufacturers and phone service providers create equipment which all talks together and functions well. That said some countries use different frequencies to broadcast compared to other countries so there are different frequencies of GSM just as there are different frequencies of CDMA phones. There are various duel band, triband, and quad band (world band) phones which are designed to work in multiple areas.

Obviously the more features the phone has the more expensive it is likely to be but I find it is valuable to have an unlocked world band phone and a second prepaid simm card if I am traveling over seas. That way I don't pay roaming charges though it does mean my phone number is different while I have the second (local) simm in my phone.

[DanS]

Do you or anybody else from Poly in the US use an unlocked phone?

[Dinner]

Yes

Though the truth is I didn't buy my phone directly from a provider and instead got it from a third party. Almost all third parties sell unlocked phones. If your phone is not unlocked then just take it to one of those independent shops and in 5 minutes they can unlock the phone for around $10.

Again, unlocking the phone just means that you can shop around to other service providers who support the standards used on the phone you own. You can't unlock a GSM phone and think it will work on a CDMA network. You'd have to choice between the providers which offer GSM networks.

The exception being if you have a multi-band phone in which case you can shop around from multiple systems.

[Dinner]

Originally posted by Oncle Boris
DanS may be right, IIUC some of the North American carriers actually provide no way to change the SIM on a phone.

The simm cards are only for GSM systems. Cell and CDMA phones use a built in chip on the phone.

[DanS]

Am I correct in understanding that a prepaid card and a sim card are separate items that are sometimes sold together?

Edit: I think I'm confused. If I buy an unlocked phone, that doesn't necessarily mean that I can insert my own sim.

[Dinner]

There are two things though they can be the same. It just depends. You can have a phone card which is a plastic card about the size of a credit card which has a code you have to enter every time you use the phone (much like a calling card) but those are unpopular and rare. What I was talking about was actually having two simm chips one for where you normally live and one for your business destination (say Japan).

If you use your regular American account/simm chip then you will get smacked in the head with giant roaming charges for using your phone in Japan. You can instead buy a pre-paid simm chip in Japan (with say $50, $100, or $200 worth of air time) and put that chip in your phone so you'd pay local rates instead of roaming rates. Once you change the chip you'd be a NTT-DoCoMo (or who ever) customer where as once you put your old simm chip back in then you'd once again be on your old provider.

The phone company is tracking the usage on that simm chip, not the phone, so if you switch simms then you are switching the phone account as far as the provider is concerned.

[Dinner]

Originally posted by DanS

Edit: I think I'm confused. If I buy an unlocked phone, that doesn't necessarily mean that I can insert my own sim.

You can always put a different simm into a GSM phone but some service providers lock the phone so that only their simms will work with the phone. If you unlock a GSM phone then you can put in the simm from any other GSM provider.

The problem is in the US there is typically only 1 or 2 GSM providers in a given area so you still won't get much choice. There maybe half a dozen other wireless providers in your area but they are likely using a different technology standard. An unlocked GSM phone will never work on a CDMA or cell network unless it is a multiband phone and the same goes for the other two. Once you unlock a phone you can choice between other service providers who use the same technology but not between service providers who use competing technology.