I thought I'd post this as while everyone seems obsessed with the lowest overall price they can get away with paying, I personally just want a good combination of phone and tarriff since I'm due for an upgrade shortly. This is obviously a good fiver cheaper than the deal that T-Mobile has been otherwise offering so far. Well, the handset will cost you £19.99, but that's only £20 as opposed to an extra £5 a month for 18 months (£90).
People seem happy to pay £25 a month for 300 minutes and 500MB internet access, so for me this deal is much better value as there's twice as many minutes and you'll presumably get away with more than 500MB of data on T-Mobile. The tariff is called Web 600.
Other deals at this combination of price/inclusive minutes are seemingly only available on 24 months contract. This being an 18 month contract makes it the best deal (imo) in my eyes for someone who wants the phone with a good contract, rather than just someone out for the cheapest price overall.
Please also note the phone comes with 4GB memory card and there is £50 quidco available.