My phone's getting a bit old (4S), and I'm taking this opportunity to move to T-Mobile, where the BYOD offerings are much better.

BYOD means $20 off your monthly bill (or subsidizing is +$20, whichever way you look at it), and the BYOD rate is legitimately substantially cheaper than similar plans from AT&T or Verizon.

Plus even if you subsidize the device the terms are far better. The $20/month goes towards paying off a debt, which is simply unsubsidized price - subsidized price. If you leave early you pay the remaining balance and the phone's yours. This is in stark contrast to AT&T's rather punitive early-termination fees that exceed the actual subsidization provided initially.

That seems bizarre in the UK. I pay $24/mo and get truly unlimited data, with tethering included, as well as 2000 minutes and 5000 texts (and receiving doesn't come out of your allowance in the UK, the caller pays that fee).

It's absolutely cheaper to buy devices outright here.

Example of Three's One Plan for a 32GB 5s (£):

  24 mo contract
  Device        99
  Plan          46
  24 mo total = 1203
  
  12 month contract + BYOD
  Device        629
  Plan          15
  24 mo total = 989

That sucks! I've only got experience of the UK carriers, you can get something like 600 minutes, 'unlimited' data for around £10/month here SIM-only. And on a one month contract!

Assuming you dont voice much. T-Mobile offers prepaid(bring your own phone) $30/mo unlimited 4G and SMS with 100 minutes. Assuming you always want the latest iPhone, you save about $200 per 2 year. This deal was way back before LTE availability, So it WAS a hot deal.

If you actually use most of the 5GB each month, $60/mo is competitive with what you would get from any MVNO. The MVNO plan would include tethering, but I'm told that people just use tethering on AT&T plans without paying for it.

Isn't this what ting does? Not in the US so never used it, website says it is on the "Sprint" network so I guess that means coverage is patchy?