This is an area where there's a huge amount of confusion. With any luck this article will clear a certain amount of it up.
Broadly speaking, there are two types of each model of phone. It's actually far more complicated than that with regional variants, promotional offers etc., but let's keep it simple for the moment. On the one hand, you have the phone as it was originally designed by Nokia and containing Nokia's firmware. On the other hand you have phones that are distributed not directly by Nokia or their retailers but by mobile network operators. In the latter case, the firmware installed in these phones is modified by the network operator to include their logo, links to their services and a few custom features and settings. Occasionally, network operators will also deactivate features of the original phone that they don't want you using. AT&T come straight to mind with their paid-for voice dialling service − the phone already has such a feature built in but AT&T deactivate it and make users who want it pay for their own network-based version of the same thing. Firmware that has been altered in this way is called "branded" firmware because of the operator branding to which it is subjected.
With different people involved, the release date for the firmware will be different from one variant to another. Generally speaking, the original Nokia firmware will be available for release earlier (sometimes significantly so) than branded firmware. This is because network operators have to make their alterations to the "vanilla" firmware that has already been (or is about to be) released, and then test and approve their version. Also, bear in mind that ensuring its users' phones are up to date is not the primary concern of a mobile network operator. They would much rather you bought a new phone (and renewed your contract). Users sometimes therefore have to be prepared for a long wait before their operator releases a firmware update that users of unbranded phones have long since been able to install.
Note that lifting the SIM-lock on your branded phone, ie. entering the restriction code supplied by your operator so that you can use SIM cards from competing networks, will not remove the branding. You will still have a branded phone stuffed full of, for example, T-Mobile features but you will be able to use it on O2, Vodafone or whatever.
So, as a general rule, if you have an unbranded phone you'll get firmware updates within a week or two of their release, as and when they're made available around the world. If you have a phone that you obtained through your operator then the chances are that it'll be a branded phone and you'll have to wait for your operator to approve the update before you can install it.
As with all rules, there are exceptions. Here in the UK, phones sold by the Carphone Warehouse seem to have their own product codes and, as such, are more like branded phones than generic phones. I don't know why this should be because there's no apparent branding. The only indication that something is different is the unavailability of updates because Carphone Warehouse don't bother approving them. Your only course of action here is to approach the Carphone Warehouse and ask for written permission to "debrand" your phone and have generic Nokia firmware installed. With that written permission and the phone, you go to your nearest Nokia Care Point and they'll do the necessary. Ironically, more often than not, the Carphone Warehouse is the Nokia Care Point...
Another exception that comes to mind is the USA. Phones sold over there are in fact slightly different models because of the different frequency bands used, which means that Nokia USA has to become involved, and this tends to slow things down.
The UK is another exception to the rule. UK-specific, unbranded variants of recent phones are now 2 versions behind the corresponding variants of the phones for the rest of Europe and many other parts of the world. The culprit is thought to be a third party involved with Nokia Care in the UK. Some branded variants of these phones are seeing updates before the unbranded ones, which is unacceptable since customers who paid the full price for their phones (no network subsidy) are entitled to better service than this.
Once the new firmware for your phone is available, there are three possible ways you can install it.
Firstly, there's the classic "Nokia Software Updater". In a nutshell, you run NSU, it pulls down the firmware for your particular model and variant of phone and flashes it into the phone's ROM via a USB cable. The software for this is only available for MS-Windows XP SP2 or later, so users of MacOS and other Unix-based operating systems such as GNU/Linux and FreeBSD are left out in the cold. As usual.
Then there's the "Firmware Over The Air" (FOTA) method, whereby your phone connects to the internet and pulls down the update itself without the need for a computer at all. FOTA is quicker and much more reliable than NSU because it only downloads what's changed in the firmware since the version currently installed in your phone instead of downloading full ROM images, and because it doesn't rely on a notoriously flaky and unpredictable operating system.
The only fly in the ointment here is the fact that firmware is almost always released via one method alone, and the mechanisms behind one are not aware of what's available with the other. So, for example, if an update has been released via FOTA and you run NSU, you will be told that no updates are available because NSU is not aware of what's being distributed over-the-air. Similarly, if an update is released via NSU and you check FOTA, you will also be told that no updates are available.
Just to make things that bit more confusing, there are also discrepancies between what the "can I update" page is telling you and what NSU actually finds.
The third way to update the firmware in your phone is to take it to a Nokia Care Point and have them do it. If the phone is still within the warranty period the update will be free of charge. This said, updates are sometimes released to the public before the Nokia Care network (they use different tools to the ones made available to the public), meaning that the Care Point won't be able to help.
The whole thing is a bit shambolic, to be honest, and needs to be unified. However, as things are, it boils down to the following:
* If you have a branded phone you're in for a long wait before you get updates. Don't hold your breath.
* If you have an unbranded phone, the availability of updates is a postcode lottery.
* Once updates are available you have to look in two different locations to find them.
* Even if you're told that an update is available you might still not be able to install it due to inconsistencies in the updates database, and Nokia's Care network may not even be able to help you because they don't have the required updates.