Let's talk about @ThreeUK's "new customer via reseller" ONLY deals, and other phone contract renewal curiosities

This is kinda complicated and involves some maths, so please bear with me with this.

I am a customer of the mobile network Three, and have been for a number of years to the point where I get "you've been a customer of Three for...wow, a very long time!" whenever I phone. My latest contract for £24 a month has reached the end of its term, so I did some searching for the best deal. I used a few comparison sites and found a deal with Three for £12 a month that fell into my more-recent usage figures. There's also a similar deal but with more calls with PlusNet, who provide my home broadband (so they do a deal if you're an existing customer). Those are the only two deals that really caught my eye. But, since Three's deal is better, I thought I could get a straight-forward swap to the new plan without much faff.

OH HOW I WAS WRONG

So, the deal shown on several comparison websites for £12 is only shown on comparison websites, and not on Three's own website. So, when I mention it on the phone, I'm told that because it's a special plan for [comparison website name here], I cannot do a straight swap onto the plan. The only way to do this would be for me to convert my current SIM card into a pay-as-you-go SIM following the 30 day contract cancellation notice period. Then, I'd have to sign up as a new customer (assuming the offer is still available) and start a brand new contract. This would also involve two transfers of my phone number plus an amount of time with a pay-as-you-go SIM card in my primary phone. Not ideal.

But wait, there's more!

Because of the 30 day cancellation notification, I have to pay for an additional month on my existing plan first before signing up for a new one, which may or may not be the £12 a month one as it could be a limited time offer, or the more expensive but more calls £15 a month one.

However, there's another option. Three do have a £15 a month plan that is basically the same as the £12 a month plan, except for one important distinction: existing customers can swap to it immediately. This means, no extra month of the existing plan and no swapping to PAYG for a bit while waiting for all the shenanigans to process. But, it's £3 a month more...what is this in the grand scheme of things?

So, let's maths!

Current plan: 
Monthly: £24
12 months: £288
13 months: £312

£12 Three plan (new customers via resellers only):
Monthly: £12
12 months: £144
Final month of current: £24
Total (~13 months):  £168
Plus PAYG expenditure

Plusnet plan:
Monthly: £15
12 months: £180
Final month of current: £24
Total (~13 months): £204

£15 Three plan (existing customers allowed):
Monthly: £15
12 months: £180
13 months: £195

This makes the £12 plan £27 cheaper than the £15 plan over the course of the 13 months. It's worth mentioning at this point that the salesperson on the phone from Three was throwing around the idea that it was only £12 cheaper, but that's on the assumption that I don't let the current contract end before starting the new one, i.e. basing it on paying the first month of the £12 contract now and also the final month of the current contract, making a 12 month figure of £168 vs the 12 month figure for the £15 plan at £180. It's an easy mistake to make, but probably intentional considering this person's line of work.

Anyway, that £27 difference doesn't include anything I spend with a PAYG SIM card, which I'd have to keep hold of until my phone number transferred to it, and then sign up for a new monthly SIM, and then transfer the number again. So, could be £25 saving or less for potentially a lot of hassle, so I went for the £15 plan with Three. They've got me for another 12 months, oh well.

So, what have we learnt here?
1) Three, and possibly other networks, have deals that are only on comparison websites and not available direct.
2) By implementing intentionally broken computer systems, the aforementioned mobile networks get to avoid giving existing customers the best deal by forcing them through as many hoops as possible.
3) Remember when your contract expires so you can switch as early as possible and take the final month and cancellation period into account. This means, as soon as you have just over a month to go on your contract, look up the best deal and inform your current supplier you wish to convert to PAYG. PAC codes are valid for a month, so phone up again once you know the network you're switching to and there's less than a month to go. The £12 deal via a PAYG conversion would've been a definite deal if not for the additional month of the current contract.

My plan for next year is to request a cancellation just before the final month of the minimum term begins provided I'm not on the cheapest tariff for me. Then I can just join my favourite and swap with minimal disruption and maximum savings. A half hour phone call to Three's retention team taking up my entire lunch break is not something I want to do again.