The two 'hero' devices, whose debut follows the formal launch of the Windows Phone 8 platform earlier this week, both enjoy a top-end spec list.
The Lumia 920 is available exclusively on the EE network in the UK - formed from the merger of the operators T-Mobile and Orange - and will work with EE's recently launched 4G network. The handset will also be available on non-4G contracts on the Orange or T-Mobile networks, through EE stores or Phones4U, Nokia said.
A Nokia spokesman confirmed to ZDNet on Wednesday that the device would remain an EE exclusive until "at least" the start of 2013, and possibly beyond.
On EE, the lowest up-front cost option to get your hands on the device is £19.99, on a two-year, £46 per month contract. The £46 EE contract comes with unlimited calls and texts, and 3GB of data usage.
The 920 is also available on a £36 per month option, which comes with just 500MB of data and increases the upfront cost of the device to £129.
The Windows Phone 8X by HTC — which also comes in a 4G LTE variant, but not in the UK — also went on sale on Friday.
Ahead of the introduction of the device, HTC said it would be available for pre-order from Carphone Warehouse, Phones4U and Three, but at the time of the writing none of the retailers websites were yet offering the device.
However, O2 does have it available to buy, from free on a 24-month contract of £32 per month or more, or for £16.50 per month with a £150 upfront cost. SIM-free the device costs £380.
The introduction of the two 'hero' devices marks the arrival of the first Windows Phone 8 devices into the market, at a critical time for both Microsoft and Nokia: both need to make up time and market share against smartphone rivals.