http://www.callwave.com
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Callwave's Internet Answering Machine (IAM) is a software download for Windows-based PCs which captures incoming phone calls which may otherwise be missed while the user is online. The software presents a small on-screen window that appears each time the user goes online, and allows them to see and hear messages left for them while online.

http://www.internetcallmanager.com
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Internet Call Manager (ICM) is the cost-effective solution to the problem of missed calls while your phone line is busy because you're on the Internet. It is ideal for anyone who wants the freedom to be on-line. You can comfortably do everything you do on the Internet worry-free while ICM monitors your telephone line. ICM can even transfer your calls to any number in the United States or Canada - fast and easy. FREE TRIAL.

http://www.pagoo.com
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Pagoo Internet Call Waiting (ICW) is the ideal solution for anybody who worries about missing phone calls while online. When someone calls your home phone number, Pagoo takes your caller's voice message and instantly delivers it to your computer -- you play it back instantly. No more missed calls, no more busy signals. Pagoo Internet Call Waiting lets you stay in touch when you're online. FREE 30 Day Trial.