UK mobile operator EE is to boost its retail footprint by a sixth through an extension of its partnership with supermarket chain Sainsbury's.

Owned by UK fixed-line incumbent BT Group plc (NYSE: BT; London: BTA), EE said it would open another 100 stores by the end of 2019, increasing its total retail presence to about 700 stores up and down the UK.

Sainsbury's will effectively host those new stores inside its own supermarkets or in branches of Argos, a high street retailer it owns.

The deal builds on an existing agreement between EE and Sainsbury's under which a small number of phone stores have been opened inside Argos branches.

The latest move will lead to the creation of another 400 customer service roles in Sainsbury's and Argos stores across the UK, said EE in a statement.

The operator says its aim is to ensure that about 95% of UK consumers are within a 20-minute drive of an EE store.

It is also set to launch several new store formats, including "showcase" stores that will let customers try out new technologies, pop-up shops and cabins aimed at large shopping centers and "mobile EE shops in vans" for remote areas.

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EE said it had also been making improvements to its customer service capabilities over the past year.

"I know our customers prefer to talk to real people in our UK and Ireland call centers rather than receiving help from a bot, which is where many other companies are investing," said Marc Allera, EE's CEO, in a company statement. "We're investing in more people in our customer service teams, more stores for them to serve customers from, and exciting new technology that will help our teams provide even better service."

The first of EE's "showcase" stores will open in August, said the operator, following a redesign of existing premises.

— Iain Morris, , News Editor, Light Reading