Dilemma: To keep l/line or cancel.

spark_deals

In July 2009, o2 and orange ran promotion of free broadband with contract phone. Was with o2 already and they were not able to offer me. Explored about disconnecting and reconnecting. CSR advised of 6 months. So, went with orange.
Orange contract is ending on New Year's day. Orange is offering croppy phone deals as I never over-spent my limits. ~(bought the contract with minutes to match my requirements)~
I am with o2 mobile £15 SIM only with 600 minutes and UL data and texts. (got £100 cashback)
I bought t-mobile £7.50 SIM only with 600 minutes and UL texts and 3 GB data.
I was thinking to get orange canary £15 SIM only with 600 minutes and UL texts. (with £121 cashback from TCB), otherwise stuck with racoon 25with 200 minutes, UL texts and UL l/lines.
Although orange would not extend the BB to the new canary SIM only contract but my maths says that:

IF I go for TCB orange offer, it would cost me £59 for a year. (after cashback)
O2 would cost me £80 for a year.(after cashback)
T-mobile would cost me £90 a year.(No cashback)
BT l/line would cost £165 a year, (No cashback)with free orange BB.
It would cost me £300 for a year if I keep free orange BB, 200 minutes deal (maybe few extra loyality) minutes

As I understand this, Going with orange for free BB would cost=
(BT rental+ orange racoon25) 300+165= £465.

If I go other way,
T-mobile 3 GB allowance and internet dongle would cost =90 + 20=£110.

Total cost:
O2 (after cashback) = £80 (600 x net + UL L/l + UL Data + UL texts)
Orange (after cashback) = £59 (600 x net + UL texts)
T-mobile (no cashback) = £90 (600 x net + UL L/l + 3GB Data + 500 texts)

All this adds up to = £229

Hence, total savings= £465-£229= £236.

Is there any mathematics I am doing wrong?

Please point.
Thanks
Spark


Edit: I bought t-mobile £7.50 SIM only with 600 minutes and UL texts and 3 GB data. Or should I cancel it as it has not been delivered to me yet.

PS. I am copying to mobile and home phone forums to maximise the suggestions . Mods may delete and please pm me after deletion.

kwikbreaks

You are not comparing like with like. Even the abysmal Orange ADSL is likely to out-perform any 3G broadband.

It also isn't safe to assume that any 3G broadband will work where you need it as the coverage maps are outright lies. The only way to know is by trying it out.

spark_deals

Thank you Kwikbreaks.
I am not comparing like-for-like. I am comparing the savings. 3G is quite good where I live. I plan to put SIM into usb dongle for internet and phone for calls. I am not into gaming. All I use the BB for internet surfing ,e-mails and skype.
3G from o2 is being used on nokia 5800, was tested on Samsung tocco ultra. Speed was not bad. Though, I had to test t-mobile 3g yet.
Thanks