TELSTRA is sending Queensland customers an NBN-ready modem in what critics say is an attempt to "fool" them into staying with the telco without shopping around first.

For Telstra customers, boxes have been arriving on doorsteps with instructions on how to install it.

Consumer advocates warn it is a way for the dominant telco to keep a hold on its customers, rather than risk them finding a better deal.

Plugging in the modem gives customers access to the NBN through Telstra, with no change to pricing and download limits.

The modem is supplied for free, but it may also cost customers any potential savings - even from Telstra itself -- unless they seek them out.

The marketing effort has gotten the nod from the ACCC, however it is warning customers to read terms and conditions before plugging in.

Tom Godfrey from consumer advocates CHOICE told customers not to be "fooled" by Telstra's effort to keep them on the same deal unless they had shopped around.

"Although having a new modem land on the doorstep might work for some people, signing up for NBN with Telstra is probably not the best option," he said.

"Before locking yourself into a new contract, find out when the NBN is coming to your area and surf around for the best deal."

The email being dispatched to households with a modem from Telstra. Personal details have been removed.
The email being dispatched to households with a modem from Telstra. Personal details have been removed. Supplied

For those not wanting one of Telstra's NBN packages, the telco asks them to mail back the modem, with the box unopened.

TPG's chief operating officer said the modem mail-out was an attempt by the TPG competitor to "sew up its own customer base".

He said Telstra wanted to draw the most money from users "by locking down customers early on in a manner that is not transparent to the average consumer".

TPG won the 2016 Canstar Blue NBN provider award for customer satisfaction, network quality and value. The year before it was won by iiNet.

Canstar Blue ranks Telstra the lowest of five providers, ranking it below iiNet, Dodo, Optus and TPG in categories including speed, value, and "contract clarity".

Telstra has defended the campaign and has said it was about helping customers on to the NBN "as quick and easy as possible".

A spokesman said if customers were not on a contract, having the extra modem would not mean extra charges if they opted to leave Telstra.

Those still on a Telstra contract would face the usual fees for breaking an agreement if they go elsewhere.

The ACCC has released guidelines for finding the best NBN deal.