I went from Vodafone.
It works perfectly now, but I had a problem during the first week: I was not able to get/receive calls or texts.
All you need to do is upgrade your phone number manually in your phone settings(= rewrite your phone number starting with +44).
Wonderful Sandra from the customer support team sent me a detailed explanation on how to do it because I am not familiar with technology.
Do not be afraid to change a mobile provider. It is a bit cheaper than Vodafone. But be aware that you may need to upgrade your phone number after this.
Sundra from customer support is the best person I've spoken with in the last few years.
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