With significant savings on both monthly contracts and SIM-free handsets, smartphones are among the most popular purchases to make on Black Friday. For 2015, many networks and retailers have opted to offer Black Friday and Cyber Monday deals for several days, instead of over one 24-hour period.

As a result, we're able to bring you some of the hottest smartphone deals already, four days before Black Friday itself. Deals are a little thin on the ground right now, but we'll be updating this article - and all of our other Black Friday pages - throughout the week.

First up, here is what GiffGaff has to offer. These are all contract-free prices:

Black Friday prices:

Samsung S6: £299: (£100 off)
Samsung S6 Edge: £399 (£100 off)
Samsung S6 Edge+: £479 (£100 off)
Sony Z5 Compact: £329 (£100 off)

Next up, it's Carphone Warehouse:

• Samsung Galaxy S6 (32 GB) available on Vodafone for free at £22 per month inc. 500 mins, unlimited texts, 500 MB data (a £200 saving on the upfront cost of the handset).

• Samsung Galaxy S6 Edge (32 GB) available on EE for £50 at £32.49 per month inc. unlimited mins, unlimited texts, 5 GB data (a £100 saving on the upfront cost of the handset)

• HTC A9 available on O2 for free at £23.50 per month inc. 500 mins, unlimited texts, 500 MB data (a £200 saving on the upfront cost of the handset)

• Huawei P8 Lite available for free at £9.50 per month inc. 300 mins, 5000 texts, 500 MB data (a £200 saving over the life of the contract)

For more Black Friday deals and discounts, visit the IBTimes UK Black Friday hub

And here are the best offers from Three. They are a bit vague for now, but come Friday morning the website will have all of the details you need.

  • £121 off Samsung Galaxy S6 Edge
  • £125 off Samsung Galaxy S6
  • £60 off the Moto G third generation, with Moto Maker, making it £99.99
  • Up to £216 off the Samsung Galaxy Alpha
  • Up to £168 off the Acer E3
  • Up to £144 off the LG G3
  • Up to £72 off the Microsoft Lumia 635

Vmall, the official retailer of Huawei and Honor phones in the UK, will be offering Black Friday details, but not until the day itself, when its website opens for business at 9:30am. In the meantime, if you register with the site you get a free voucher which takes £40 off the price of the Honor 7, currently priced at £250.

Mobiles.co.uk has jumped the gun, with a number of Black Friday deals already available. These include:

Vodafone says it will be adding some Black Friday deals to its website soon.

O2 will be adding Black Friday deals to its website on 26 November

EE's website will feature Black Friday deals on 27 November

Amazon only has a couple of smartphones on sale in its Black Friday section for now, but this will change on a daily basis, so it's definitely a website worth keeping an eye on. They are:

This article will be updated with more Black Friday deals as they appear online over the coming week.

As part of its Black Tag sales event, Currys is selling the 32GB Samsung Galaxy S6 for £250 SIM-free, a £130 saving.

Black Friday 2015: How to get the best deals online IBTimes UK