Love 'em!
Been with them for coming up to 2 years, since my O2 contract ended. Ordered a sim, which arrived in a couple of days in a funky package. Got my number ported, which took another couple of days, since then I haven't looked back.
Pros:
-Ridiculously cheap tariffs
-O2 network coverage
-Forums full of advice (average answer time < 45mins
-Goody bag system (now reoccuring)
-Unlimited data
-PAYBACK!
Cons:
-No telephone customer support
-No handsets or insurance
-iPhones cannot use the inbuilt voicemail function (work around with HulloMail)
-Forums full of complaints
To put it in perspective, my O2 contract was £35 per month for 1000 mins and 500 texts, I had to have the bolt on of 500 texts (was going through that phase of texting) + unlimited data. That had on top of it handset insurance of £15 p/m. For some reason though my bills were always north of £60.
Since then, I haven't spend more than £15 p/m with GiffGaff.
How it works:
Get a Sim card, there are literally hundreds of members on the forums who are effectively 'giving' away cards. The whole network runs off the ethos that it really is run by you. You can order cards directly from GG but they like their members to give them away. The bonus being, if you use a members card and sign up, you get 500 Payback points and so does the member who gave it to you.
Whack the Sim card in any unlocked or O2 handset. If you want to keep your number then you'll need a PUK code from your current network, you then pass this onto the 'helpers' at GiffGaff who will port your number.
GiffGaff can work in two ways, you can either treat it as a Pay as you Go network by buying credit and spending it as much as you want, OR buy a Goody Bag which has a bundle of credit, texts and data allowances...
£5 - 60min - 300 texts - No data
£10 - 250min - Unlimited texts - 1GB Data
£12 - 250min - Unlimited texts - Unlimited Data
£15 - 400min - Unlimited texts - Unlimited Data
£20 - 800min - Unlimited texts - Unlimited Data
£25 - 1500min - Unlimited texts - Unlimited Data
A Goody Bag lasts a month and after that you have the option of buying (queuing) another one, or one of a different level, or just not. Only recently they've just started doing 'reoccurring Goody Bags' so you can effectively run a contract phone.
If you do go down the goody bag route, you'll also need to put say £10 on credit in case you have to ring any premium rate numbers. I have only had to do this a couple of times, and it generally gets used up around insurance renewal time on the phone to companies. This can also be set to automatically top up, so you never need to worry about running out of credit mid call.
Payback:
Payback is pretty unique to GG in the way that they pay you to use their forums and support other members. The more you input the more payback you earn. To give you some idea, last December at Payback time, I got Paypal'd from GG £40 to which I used on eBay. It can be paid back as money, or turned into airtime credit or donated to the charity as chosen on the forum.
The Community (Forum)
Take the forum with a pinch of salt. Sadly, as its where everyone goes for advice, so it will always seem like everything is going wrong. But most problems are solved on the forum, and it also has some pretty funny banter.