Hello.
Sorry, it's not entirely clear what you are asking.
If you are asking about carrier billing, paying for services or buying things through your Three phone bill, the Spend Limit doesn't have any effect on those. You can have a spend limit of £0 and you'd still be able to use your phone for carrier billing.
Carrier Billing has a limit of £40 per transaction, and £240 total each billing cycle. You can limit carrier billing by contacting the front line team on 333, or by using Livechat on our web page and asking them to set a Credit Limit on your account.
If I've not understood your question correctly, please let me know and I'll do my best to get you some answers.
Pete.
