The firm says customers are now getting normal service following a technical failure that hit hundreds of thousands of customers.
Most reported problems:
BT says services have been fully restored after a crash that affected broadband customers across the UK.
The communications firm's website and customer service platforms were affected by the glitch on Tuesday, blamed on a "technical issue". It has ruled out any suggestion of a "malicious attack".
A statement on Wedneday said: "BT is confident that services have been fully restored following an outage that affected several hundred thousand customers yesterday.
"A faulty router was to blame for the outage and we apologise to those customers who were affected.
"Most customers will be able to access their broadband without taking any action but some may need to reboot their equipment. for more information they may contact here"
Social media users first started reporting problems at 2.30pm and customers took to Twitter to relay their experiences.
One, Keith Pestell, tweeted: "BT internet down, support lines down and website down. I did get through to India and the lady said: It's working here... really?".
Another, Char X, said: "What's happened with #BT? Internet down, help numbers not working and every page leads me to an error on the website!!!"
The Down Detector service, which monitors internet-based failures, noted thousands of customers in major cities reporting faults.
BT said it had managed to restore services to most customers within a period of approximately two hours.