United Kingdom

Vodafone UK
Vodafone has a "Pay as you Go" service.

More information

Data feature packs

 * 50p for 25MB per day
 * £5 for 250MB for 30 days
 * £10 for 500MB for 30 days

Availability
Purchase a SIM card from any Vodafone store for £5, which includes some calls. You can recharge it at their stores or many other kiosks or convenience stores throughout the country.

SIM sizes

Standard SIMs are freely available, but in Jul-Aug 2011 Micro-SIMs for PAYG were generally unavailable from most Vodafone stores throughout the UK. However, Standard SIMs can easily be trimmed down with scissors to fit the iPhone 4.

Tips
Check first for compability with your device. Vodafone "Pay as you Go" SIM cards with data packs only work on specific "Pay as you Go" devices (tried in Q4/2010 with "3 MiFi Mobile Wireless Modem" and "Vodafone Huawei E220 UMTS Modem" - confirmed by Vodafone UK customer support)!

 iPhone 4 users  will have to change the default APN settings before activating the data on Vodafone. If not, the phone will give the error "Could not activate cellular data network". The correct setting can be found on Vodafone support.

Default data rate

 * 30p per MB

More information (This is only for smartphones.)

Data feature packs
When data is used up you are free to buy another pack without waiting until the end of the previously bought add on pack. After data add on is used up charges revert to 30p per MB if another add on is not bought.
 * 150MB valid for 90 days with every top-up
 * 120MB valid for 1 day for 50p
 * 500MB valid for 30 days for £5

More information (This is only for smartphones.)

They also do an Unlimited data PAYG deal for £15 for 30 days that includes 300 minutes and 3000 texts. However, to get this deal you MUST first topup your account with the £15 and then CONVERT the £15 credit to an Add-on, otherwise you'll be paying the default data rate of 30p per Mb. You can do this online once you've created an online account with 3.

You can recharge using a credit card, but only if your credit card has a UK postal address.

More information (This is only for smartphones.)

Availability
Purchase from a 3 Mobile store for £10 which includes £10 credit, also available online. Extra credit can be bought from anywhere displaying the green 'top up' logo.

Mobile Broadband

Use the iPad data plan with 1 GB (£10.49) or 3 GB (£20.99). Valid for 30 days. Top-ups: 1GB £10, 3GB £15, 7GB £25. Link to iPad data plans

Link to Mobile Broadband with dongle and SIM only

SIM sizes
Mini SIMs as standard. Micro SIMs may be available on request, (mini SIMs are able to be cut down to micro SIM size).

Frequency

 * WCDMA 2100

Tethering
Yes.

Other Notes
As 3 Mobile is a purely 3G network a 3G mobile phone (with the 3G function turned on) is required, a 2G mobile phone will be cut off.

Default data rate
Free SIM. £1 / day. See link for more information.

Data feature packs
See link for more information, or see the gallery below.
 * 5 days: £2.5. Text WEB to 441
 * 1 month: £5. Text MONTHWEB to 441
 * 6 months: £20. Text 6MONTHWEB to 441

Fair use policy
Browse and email as much as you want. Streaming has a limit. The default data rate comes with a fair use limit of 40 MB a day. The 5 days, 1 month and 6 months have a limit of 500 MB (per month in the case of the 6 month version).

Availability
T-Mobile SIMs can be obtained for free in their own shops

SIM sizes
Mini SIMs exist. Micro SIM available in at least one store (out of one) sampled - in cambridge.

Frequency

 * GSM 1800
 * WCDMA 2100

Tethering
Yes (tested with a Nexus One / Froyo). Iphone 4 did not offer tethering with the 5 pounds a month pack, however personal hotspot feature is available.

Additional
T-Mobile are currently running a promotion that allows you to get 6 months of free internet access if you buy a selected PAYG handset. The cheapest selected handset is 19.99, so buy the handset, get the promotion & put the SIM in your handset of choice. (The offer is valid until 31st August.)

Orange
Orange has a "Pay as you Go" service with a free sim card.

More Information

Default Data Rate
Maximum £2 per day

Data feature packs

 * £5 for 250MB prepaid data for 30 days
 * The Dolphin plan gives 100MB data a month

Availability
Purchase from any Orange store for free. You can charge it at their stores or several other kiosks in the country. Top up online easily.

If you are an overseas visitor, getting the Camel plan instead of Dolphin makes more sense. Paying £30 top up will give 240 free minutes international calls & cheap international calls after this. So works well coupled with the 250MB data extra.

Default Data Rate
£3 / MB. See Simplicity T&C for more information.

Data feature packs
Choose the "Text & Web" SIM tariff. Top up the following minimum in a month and get the corresponding text (to UK numbers only) and data allowance for 30 days, and calls/international text to the value of the amount of top-up. Further data allowance is available in the form of a "Web Bolt-On": £3 for 100MB, £6 for 500MB and £10 for 1GB. Text "WEB" to 21300.
 * £10: 500MB + 300 texts.
 * £15: 500MB + 500 texts.
 * £30: 500MB + Unlimited texts.

If you don't have a web allowance included in your tariff, or you don't have a web Bolt On or have not topped up a minimum of £10 with the Text & Web tariff, you'll be charged up to £1 a day to view the internet on your mobile.

Fair use policy
Unclear. The terms and conditions state that there is an excessive use policy, but not how much or for how long.

Availability
O2 Simplicity SIMs can be ordered for free from O2's website to UK addresses only or from an O2 store.

SIM sizes
Mini SIMs available. Micro SIMs can be ordered for Simplicity customers or picked up in-store.

Frequency

 * GSM 900
 * GSM 1800
 * WCDMA 2100

Tethering
Not available with iPhone.

Default Data Rate
50p / MB.

Data feature packs
There are no packs or plans. Just one flat rate.

Fair use policy
Unclear.

Availability
Can be purchased online or from select ASDA supermarkets.

SIM sizes
Stock standard SIMs.

Network information
Branded as ASDA - Uses Vodafone network.

Frequency

 * GSM 900
 * GSM 1800
 * WCDMA 2100

Tethering

 * Unknown

Default data rate
30p / day

Data feature packs
See this page for more information.
 * 1 month: £5.

Fair use policy
The default data rate comes with a fair use limit of 25 MB a day. The 1 month data pack has a limit of 1 GB.

Availability
Virgin mobile SIMs can be ordered online for free or in shops.

SIM sizes
Stock standard SIMs.

Frequency

 * GSM 1800
 * WCDMA 2100

(uses T-Mobile network)

Tethering
unknown

Default data rate

 * 100 MB per day, free until 28th February 2011
 * 20p per MB to 2.5MB capped at 50p per day up to 30 MB, then 20p / MB for further usage that day.

Data feature packs
See this page for more information.
 * 1 month: £10. unlimited data, unlimited texts, 100 minutes voice (special offer 250 minutes until 1st january 2011)

Fair use policy
The free data until 28th February 2011 has a fair use limit of 100 MB a day. The 1 month data pack is explicitly unlimited.

Availability
GiffGaff SIMs can be ordered online for free.

or with £5 free credit on activation from jahplay@gmail.com or any other member of giffgaff. The member him/herself also receives 500 points worth £5 of balance on activation of the new SIM.

SIM sizes
Stock standard SIMs.

Tethering
Officially against ToS, although this policy does not seem to be strictly enforced, unless abused. Tested working with HTC Desire.

Default Data Rate
£4 / MB.

Data feature packs
monthly plan: £10. unlimited data for 3 months (fair use 500MB), unlimited texts, 250 minutes voice

monthly plan: £15. unlimited data (fair use 500MB), unlimited texts, 500 minutes voice

Fair use policy
T&C don't allow P2P, VOIP and continuos streaming AV and use SIM cards i modems (I haven't check that yet)