As of 2013, I have two SIMs for 3G data, with the built-in WWAN card on my ThinkPad. I use SSH tunneling to gain compression and reduce usage in both cases.
Back in the old days…
Well, I got an unlocked Sierra Wireless Aircard 750 off Ebay (PCMCIA GSM+GPRS datacard). Then I needed a SIM and a network connection to use it with; in the UK there are two ways of signing-up the first being contracts paid in arrears (at the end of a month) for the cost of the `line' plus the sum of the calls made in the previous month. The second method is pre-paid systems, where you signup with a mobile phone-company and purchase `credit'; that is, you pay up front for a certain volume of calls and need to ``top-up'' when you pre-paid credit runs out.
There are a number of caveats; with the contract system a data-tariff is often available only on top of an existing voice contract. This means that you may be paying upwards of £20.00 per month (£15 voice plus £5 data) before you even download a single byte of data; with a PCMCIA card that can't even make voice calls this doesn't make sense! Vodafone are the only people in the UK to offer a data-only tariff and this costs £5.00+VAT (£5.87) per month. On the pre-pay side one gotcha is that some networks require you to top-up with £10.00/month (eg. You need to spent at least that per month or your phone gets cut-off). Pre-paid GPRS costs are from £4.00-£10.00/MB).
Pre-paid Orange PAYG (Pay-As-You-Go) had the cheapest per-MB rate for GPRS and no limitation on ``roll-over'' (being able to use your credit over as long a period as you need). I wasn't keen on signing up for a 12month contract as I'm hoping/expecting 3G (Next-generation UMTS) data-rates to start being affordable in early 2004. Much to my surprise, pre-paid came out cheaper for the usage I'm expecting to use. Here are the figures I'm working with; I've already discarded all the other networks' offerings as they didn't work-out cost effective:
|£20.00||£0.00||0 MB||£4.00||Orange PAYG|
|£0.00||£5.88||0 MB||£2.35||Vodafone Contract|
To further complicate matters. Firstly, the Vodafone offers are quoted without VAT, hence £2.00→£2.35 and £5.00→£5.88. Secondly, I purchased a new Orange PAYG SIM on Ebay for £9.75; including delivery and which came with £1.00 included (effectively £8.75). Thirdly, if you buy greater than £50.00 worth of PAYG credit Orange give you 10% on top, bringing the effective cost down from £4.00/MB to £3.64/MB. Revised costings:
Adding together the rental cost (or the one-off cost of the SIM) and the price per MiB over a 12month period:
Calculation: 8.75 + 3.64x = 70.50 + 2.35x → 1.29x = 61.75 → x = 47.86
≤ 47.86 MB/year (< £182.96): Orange PAYG is better value
≥ 47.86 MB/year (> £182.96): Vodafone Data-only Contract is better value
Occasionally (eg, when downloading a big file) it actually makes better sense to dialup at 9600-baud than use GPRS. Orange have three variations of PayAsYouGo. After doing the maths I reckon that although I thought Talk&Save works out at quite a lot for the initial three minutes on a particular day. Talk&Save is the best value for GSM dialup (for long download periods when GPRS stops competing).
|GSM Dialup||Talk&Save||FixedAllDay||ChooseOnPeak ChooseOffPeak|
 Maximum difference between Talk&Save and FixedAllDay
 Talk&Save becomes the cheapest after 6minutes
 After 12minutes of dialup, Talk&Save becomes even cheaper ``OffPeak''