^^
That is still entirely situational based on your tariff and network provider, and normally only works if you genuinely would have ended your tariff without a better upgrade deal, and can get a similar tariff on a new connection with a cheaper handset. T Mobile upgrades will still easily haggle you a good offer based on the cost of the handset at other places, they are very good at customer service. It does however work on O2, and I did do it twice before with them when I got a K700i, and K750i, the reason being that O2 upgrades wouldnt listen at all for reducing prices to match what could be had on a new deal for cheaper. However on T mobile, the upgrades people actually do listen and haggle you better prices anyway. You can still haggle a good deal on T mobile through upgrades using sim free and new connection prices as comparisons.
I wouldnt go to retentions and threaten to end a T mob 50% discounted and also discontinued tariff, they would most likely catch my bluff very easily on this current contract, and would prefer to let me cancel the tariff anyway as they already lose a lot of money on them. They actually do try to cancel these half price tariffs whenever they possibly can, they wouldnt ever give you a better deal as opposed to letting you just end it. The only thing I would go to retentions about is if upgrades tried to cancel, and wouldnt let me keep my discount, but they have let me keep it with no problems for all 3 of my upgrades so far.
You cant get £180 worth of calls, SMS, and MMS, plus 10 Gb of data limit with modem and Voip use for £28.75 anywhere, or anymore even on T mobile. T mobile know that as well - they arent thick, and to even have offered me a free X10 Mini Pro, or a HTC Desire for £110 on this tariff is brilliant enough to me, and I would have to be a whiney cry baby 6 year old if I went to retentions to try and haggle a cheaper upgrade than that
I also doubt they would have haggled the HTC desire any lower when they already have so much demand, and as upgrades replied when I asked if they could reduce it due to the wait time, they said - 'No, we really wouldnt be able to do that as we still have people that have been waiting for several months for this handset and are willing to buy them at the same price we have offered you'.
Anyway, my X10 Mini Pro just arrived:
First impression - I really cant believe how much better the UI is, and how easy the phone is to use than all the ones I've had before, even for such a small android device. Navigating on the touch screen and typing on the slide out keypad is quicker and easier than any standard T9 phone I have used before, and is far easier than I would find typing on a touch screen. The phone is also very nice nice looking, and came with all the accessories I would need, including a screen protector, case, and 2 Gb Micro SD, although I already have an 8 Gb one.