I've had a BT broadband line for around 5 years. I was told I need to upgrade the modem to take advantage of the new fiber-optic line.
A new modem has now been delivered, but it says the new contract will only start in 2 weeks. Can I install the new modem now already, or will it only work once the new contract is activated?
It would help to know what you are upgrading from - to.
Are you going from ADSL to VDSL or VDSL to FTTP?
For FTTP an engineer is needed to install the Fibre cable and ONT. For the other sevices you will receive a hub which is standard across all copper services.
Welcome to this user forum.
If is a normal connection that uses your phone line, then you can plug it in whenever you want, but you would not see an increase in speed until after the upgrade.