Think about it: I call and send texts in roughly equal measure (in terms of how much I pay for them), so if I did not exceed my Vodafone credit of 350 CZK by a single cent, it would get me 147 texts and 34 minutes of calls. With Vodafone I would pay 89 + 134 for 150MB of Internet = 223 CZK.
On top of that comes a second data plan with O2, where I have a 1GB FUP, but you cannot make calls from this SIM card. I only have it because with O2 the speed does not drop to 16kb/s like with VF/TM, but to 200kb/s. With Tesco Mobile, using the double credit offer, I would pay: voice services 49.3 + text services 110.25 + 150MB of Internet 150 = 309.55. The result?
With Tesco Mobile I pay less, even though I get a 75% discount on my 350 CZK Vodafone credit. I will be able to get rid of one phone and one data plan, and even if I use up the 150MB FUP with Tesco Mobile, my speed will not drop to a drastic 16kb/s. And most importantly, if someone else has Tesco Mobile, I will pay even less for voice services, because calls to Tesco Mobile cost me just 1.5 CZK per minute (with double credit 0.75 CZK), and calls to other networks 2.9 CZK/minute.
So I could give my mom my dumb Nokia, which takes 2 SIM cards, and buy her a Tesco Mobile card, which would save me even more, and a minute of calling would cost me the same as 1 text message. And the best part, the thing that finally won me over: the double credit bonus on every top-up when you link your number to a ClubCard has been extended until the end of 2014!
The bonus credit has to be used within 30 days of the top-up and is spent first. That would mean I would buy Internet for 150 CZK each month and use up to 50 CZK on calls and texts, and I would keep the 200 CZK of “non-bonus” credit for the next month. Looks good.
I think I probably will not find a better offer. Either the virtual operator is too small and I do not trust it not to shut down soon, or it has cheap calls but its data services are a 2 out of 10.