>>VNC is great. There are clients/hosts for Windows, Unix, Pocket PC. It is free as well.
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>VNC is great but it does not provide any file transfer function. Is there any freeware that provides us with a file transfer function over the Internet. It will be great if I can tell my client over the phone to download and install a simple utility so that I can transfer a file to him.

You could email the file to the client, then use VNC to open and install it on the client.