The display phones at the Three store in High Wycombe have been removed, only to be replaced by 16 of their edible counterparts.
Each creation mirrors the store's products to the finest detail, with the screen colours and features clearly visible, and their cake-like texture revealed when cut open.
The sponge cakes, which are a mixture of chocolate and vanilla flavours, will remain in-store for the duration of the day.
The GBBO final airs at 8pm on BBC One, where one of the three finalists - Nadiya Hussain, Ian Cumming or Tamal Ray, will be crowned winner of the 2015 series.
A Three spokesperson told Event: "To get in the baking spirit ahead of tonight's final, we’ve made it right for fans of the show by producing our own show-stopping cake display in Mary Berry's hometown store, worthy of any star baker award.
"It certainly brings a whole new meaning to our 'all you can eat' tariffs, while acting as a great example of an experiential stunt designed to create topical social content!"
In other recent news, Three sent a fleet of Downton Abbey-themed cabs out onto the streets of London last month, to celebrate the launch of the period drama's final series.