In the end I didn't wait until early August to switch my mobile phone provider from Vodafone to BT Mobile. A friend prompted me to act now.
I did it late last night. It turned out to be easy.
I simply delved into the support pages on the Vodafone website, and studied what they said there. I got hold of a PAC, the code you need when you want to switch provider and take your existing mobile phone number with you.
Then I logged onto the BT website - I'm already with BT as a broadband customer - and worked through the very attractive SIM-only offer I had my eye on. After giving BT that PAC, I went ahead and completed the order. The £15 a month I'll now be paying (for a 12GB SIM) will simply be added to my ordinary monthly BT bill. I'll be paying for broadband and the mobile phone service together. So far as I can see, this new combined payment will commence with my next BT bill in early August.
Meanwhile, in the next couple of days, a shiny new SIM card will wing its way from BT. On receipt, I just pop it into my phone, use the Network Unlocking Code I've already obtained from Vodafone, and - hey presto! - I should get a mobile phone service from BT, using the EE network. I have every reason to think EE's service will be better for my needs than Vodafone's OK-but-not-brilliant service. Certainly rather cheaper, on the particular deal I've gone for.
Initially I'll be allocated a temporary mobile number, but within at most 24 hours I should be switched to my usual number, ported from Vodafone. For that brief interlude I can phone out, and text, but won't be able to receive any calls and texts - unless I give the temporary number to people who might want to get in touch. I can still get emails, of course.
So what about final billing at Vodafone? Well, I'm ending the two-year contract with them four weeks early, so there's an Early Termination Fee. And I have to pay for the period from the last billing date to the disconnection date. This translates into a final bill of £60 or so in mid-August. No surprise there. It means that in August I get two mobile phone bills, Vodafone's and BT's, but I can handle it.
I shall soon forget all about Vodafone taking their pound of flesh. By switching now, I qualify for BT's current freebies - the fancy JBL bluetooth speaker, plus a £65 BT Reward Card. (This is a fixed-value, single-use credit card. I'm thinking I might be able to put it towards a pair of bluetooth earphones)
So all in all, an excellent outcome - provided the switchover goes smoothly. Fingers crossed on that.
Next day (Wednesday)
It's fourteen hours since I took the plunge and set things in motion with BT Mobile. So far, so good. My BT account is now showing both the broadband and the mobile phone services. That temporary mobile number is shown there too.
I've also had an email telling me that my new SIM card is on its way and will arrive in two days' time, on Friday, which is convenient as I can continue to use my regular phone number with Vodafone until after Friday lunchtime. (Even a brief time on a temporary number would be inconvenient, as my friends wouldn't know that number, and couldn't call or text me) Swapping SIMs on Friday afternoon, with a number-port happening overnight, would mean being 'live' with BT Mobile, using the correct mobile number, by Saturday morning.