What is your policy re ISP accounts?

We are about to upgrade our remote access capabilities from RAS to VPN and/or Outlook Web Access (OWA). This means that people will require an ISP account. We want to put a policy in place before launching OWA/VPN to ensure that we don’t end up paying for 500 ISP accounts. Does your company have a policy regarding who’s accounts are paid for, and how much? Thanks.