My spare phone is on the cheapest network there is ... bar none.
I very rarely text and I dont use more that 200 minutes worth of voice calls a month. My employer gives me a phone I can use nearly all the time so I use there credit/contract.
My spare phone is on the Ovivo freedom plan.
http://www.ovivomobile.com/
Initial layout is £20 .... this gives me a new sim card and £15 of credit.
The £15 of credit gives me 200 minutes and 300 texts every month.
Every month thereafter I get 200 minutes and 300 texts added to my account ... at no cost !
As long as you dont exceed this allowance your minutes ant texts are free every month.
So since joining Ovivo my phone has cost me nothing other than the initial £20 and I still have £15 credit.
Ovivo use the Vodaphone network and the customer service is second to none.
If you are a low user (less than 200 minutes per month) there really is'nt another choice to make.
So where's the catch you say ... there isn't one. All you need is any sim free
smart phone... forgot to mention you also get 500mb of data free on the freedom plan.
If you use the data, every now and then you get an advert on your browser to watch. Be like me and dont use the data and you dont have to watch it.
I've now got two of these sims and 2 smart phones this gives me 400 free minutes a month ... I have no use for a landline other than for broadband.