I am a smarty customer.
The unlimited everything deal is now £18 a month. No contract. It just renews each month.
Bargain!
Slightly cheaper than Three, by about £2 to £4 per month. But my goodness, you lose out on Smarty!
The IP address you get is not public routeable one, as you get on Three. Not a big deal for many people, but if you are monitoring anything in your van, you can use ddns on Three, but not on Smarty.
More significantly, I found that on Smarty, each time I connected I was allocated an IP address, and within a minute or two, it switched to the next IP address up, leaving any ftp or ssh connections just hanging until they timed out.
Then a minute or two later, it switched back to the first IP.
Smarty support were unable to help, just reiterating that "you don't get a fixed IP on Smarty" - I didn't expect a fixed IP, but I did expect a stable IP.
I was able to return the sim card for a refund (I hope: the refund is due soon at the end of the first contracted month).
Smarty's unlimited calls and text deal with up to 3GB of data for £8 per month is excellent value.
You get up to £3 back each month if you don't use your data allowance. So that's unlimited calls for a fiver a month!
I reckon that the Smarty unlimited data offering is so inferior to Three's that it's not worth the tiny saving.