But the deal is only available to the firm's existing broadband customers, and those who sign up for a broadband deal.
There are no download limits and TalkTalk has pledged that speeds will not be impaired during peak times.
Customers can use as much internet as they want, without the fear of being charged extra for overzealous use.
The contract length is one of the shortest on the market and compared to other providers and can offer savings in excess of £200 when taken out over an 18 month duration.
TalkTalk says a like-for-like unlimited data plan from Three over 18 months would set you back £27 a month. If opting for the TalkTalk SIM instead, customers could benefit from a saving of £270 over the year and a half.
The deal is only available to the firm's existing broadband customers, and those who sign up for a broadband deal
If you take up the All-in SIM but cancel your broadband, TV, or call package the price and terms of the contract will be adjusted.
The cost of the SIM will rise to £24 a month and the package will be limited to 2000 minutes, unlimited texts and 2GB of data a month - showing that in some cases, it pays to be loyal.
At the end of last year, TalkTalk treated their TV and broadband customers to a free SIM as an add-on to its Plus TV, broadband and anytime calls package.
The SIM provides 100 minutes, 250 texts and 200MB of data and is worth £90. The popular move by the provider has meant that around half a million of its customer base are TalkTalk mobile users.
Please note: any rates or deals mentioned in this article were available at the time of writing. Click on a highlighted product and apply direct.