Yes, I have seen those tariffs.
This is stating the obvious, but it makes a lot more sense to use contract (over PAYG) if one can do one's
voice calls on it too. Then, especially in a business context, the firm pays for the data usage, and they can't tell if the data was all for the business
My usage is for aviation weather, flight planning and such. Using a PCMCIA GPRS card, and given that one can have just
one SIM card per phone account (I know Orange offer duplicate SIMs to corporate users with >50 phones) this makes it hard to utilise one's data account for voice, and thus get the data "on the firm".
I have a compactflash GPRS adaptor for a PDA (HP4700) which has a headset socket in it, so could be used as a mobile phone, but few PCMCIA cards can do that. It should be possible (using the PC's sound subsystem, and a Skype-style headset) but I don't know how. Constant SIM card swapping is a pain...
Of course with 3G you can run Skype directly, though I doubt it is cheaper than a mobile phone call once you go outside the free data allowance
For these reasons, a lot of people use a bluetooth+GPRS mobile phone, keep their "business" SIM card in it, and then by using the phone as their modem, they can get both data and voice "on the firm", without fiddling with SIM cards.
Personally I am on PAYG. Make too few mobile calls, and have 3 portable devices (1 laptop, 1 tablet, 1 PDA) each of which has GPRS connectivity. 4 SIM cards...
