This depends in part on who paid for the installation of phone lines (and any other start-up expenses, such as delivery/set-up of furniture) when the employee started telecommuting.

To be honest, I haven't heard this come up often enough to see any kinds of trends or policies develop. Here's my best guess, however: if the employee is moving to a new location by his/her own choice (as opposed to being transferred by the employer), and will continue in the same kind of telecommuting relationship, I think that employee would have to be prepared to pick up the costs him/herself. It wouldn't hurt to ask the company if they'd pick up perhaps half of them, but in reality, if the company paid for the installation the first time and is paying for ongoing telecom expenses, I think it's probably fair for the employee to pay for the costs of the move.

One additional factor: remember that it may not be possible to retain the same kind of broadband telecommunications service in the new location - even if you're only moving to a new home across town. The availability of ISDN, DSL, or cable modem service varies widely, so be sure to check with your local providers to determine what will be available and what the installation and ongoing costs will be.