Of course, it's not the iPhone 3GS itself that they are angry about - it's the costly terms under which they can upgrade to this handset that have led to a barrage of complaints both to O2 and on web forums and sites such as Twitter.
What's all the fuss about?
Many iPhone customers had expected O2, which has exclusive rights to the iPhone in the UK, to offer a similar deal to that which accompanied the launch of the iPhone 3G last year. It allowed first generation iPhone users to get the second generation device at a reduced fee - as long as they signed up to another 18-month contract.
This time around however, O2 expects current customers to buy out their current contracts before making the switch. For the entry level 16 Gigabyte (GB) product, which went on sale on June 19, customers will have to pay as much as £184.98, while the 32GB version costs up to a massive £274.23.
In what many would consider a double whammy, iPhone users have also been told that they will have to pay an additional £14.68 a month if they want to make use of a new tethering functionality, which allows users to connect their iPhone to a computer so that they can access the internet.
What action should customers take?
So far, there are no signs of O2 backing down on its current upgrading stance. Frustrating as it is, existing customers are therefore better off waiting out their existing contract before looking into an upgrade.
The other option, of course, is to upgrade to an alternative phone offering similar features. There is certainly no shortage of exciting new handsets to choose from. Some of the best include:
The Nokia N97: Launched on the same day as the iPhone 3GS, the N97 doubles as a mini touchscreen computer that is capable of playing music and videos, as well as accessing the web and running software from third party providers. It costs £499 without a contract, but with operator subsidies you can even get it for free.
The Nokia N86: While not a smartphone in the mould of the iPhone or the N97, the N86 is Nokia's first eight-megapixel camera phone that comes with a Carl Zeiss lens as well as HSDPA and Wi-Fi, meaning you can use it to access the internet. The handset is available through Carphone Warehouse - free of charge with selected contracts - until mid-July, after which it will also be available from O2, 3, Orange and T-Mobile.
Palm Pre: The Palm Pre, which was a huge hit in the US, will be coming to the O2 network in September. The handset, which is priced at around £125 stateside, has been dubbed the 'iPhone killer'. It includes a new information management system called Synergy that syncs the phone's contacts with Gmail and Facebook; and it combines touchscreen controls with a physical keyboard.

Cheap deals for hot handsets
You don't have to pay over the odds to pick up one of the hottest smartphones on the market as our mobile phone comparison tool shows. Here is our pick of some of the best deals available:
Blackberry 8900 Curve: Available for free with the Orange Racoon 35 tariff via Carphone Warehouse. The Racoon 35 plan includes 600 voice minutes and 500 texts for £35 a month.
Blackberry Bold 9000 Black: You can also pick up this handset for free if you sign up for the Orange Dolphin 30 tariff, which includes 400 minutes and unlimited texts for £28.80 a month. This 18month deal is available through retailer Mobiles Please.
HTC TouchHD: This handset can be obtained for free from retailer Mobiles.co.uk as part of the Orange Dolphin 30 tariff with unlimited texts and 600 minutes for just £20 a month.
It is, however, worth pointing out that when shopping around for a new handset and contract, it is vital to think first about how you are likely to use the phone. Otherwise, you could easily end up paying for services you do not need, or being penalised for exceeding your monthly call or text message limits.
For more guidance read our article 'How to choose the best mobile deal'.
Disclaimer: Please note that any rates or deals mentioned in this article were available at the time of writing.
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