It seemed a simple thing to do on paper. Ring up my mobile phone operator Three and ask to be upgraded to their new and heavily-hyped X-series data plan.

For an extra tenner a month I could get enjoy unlimited web access, unlimited Windows Live Messenger, unlimited Skype and even unlimited access to Slingbox - which lets you view your home-recorded TV programmes wirelessly on your mobile. 

That's the tantalising promise. But when I dialled up 123 and worked out which button to press on their voicemail system (Tip: If you're promoting a new service so heavily why not mention it by name on your recorded runaround) the wheels promptly fell off.

My first problem was my mobile, a Nokia N73 - pristine condition, straight from the manufacturer. According to the X-Series website this ticks every single feature box going from Sling to Skype. But it wasn't a Three-branded Nokia 73 and there's the rub.

"Can your please enter *#06#, Mr Toor," said the Indian woman, a mere six thousand miles away. I duly did as requested, thinking that by calling up my phone's serial number I would somehow be helping to get the X-series stuff up and running. (And, of course, handing Three an extra tenner a month of my hard-earned).

"You will be getting a warning letter from us shortly telling you to stop using your Three SIM card in a non-Three handset," said the woman abruptly. "If you ignore that you will get a second letter telling you that you will be cut off..."

I did my best to keep my voice level. I patiently explained that I was a journalist who reviewed a variety of different phones from day to day and that inevitably I would sometimes be using non-Three handsets.

"Look until I told you about it you had no idea what handset I was using. I only rang you up because I wanted to upgrade my service and give Three even more money every month. And you're telling me I'm a bad boy who's going to be cut off if I'm not careful."

My righteous indignation seemed to do the trick. She said she would put through the upgrade - Lucky Me! - and we would see how a non-Three Nokia N73 would cope with the X-Series plan.

Seconds after I hung up my phone rang again. It was the same woman. "The computer wouldn't let me put your Nokia in the system," she explained, with only a hint of relish in her voice.

I conceded defeat. "OK, I'll have the upgrade on my Three-branded Nokia 6280, then." I might not get Skype and Sling but I still fancied the unlimited web browsing, email and messaging.

But I'd obviously picked the wrong callcentre person to cross that day. No, Mr Toor, your Nokia 6280 is not compatible with X-series so I cannot help you. 

Would pointing out that the Nokia 6280 was on Three's list of X-series-compatible phones help me out?

Absolutely not. Her computer said otherwise and that was that. 

And I can't help thinking that on a PC monitor somewhere in a soulless refab building on the outskirts of Hyderabad there's a big red X next to the name Mat Toor.

Serves him right for trying to pay Three more money.