Your cable box service provider will provide some channels directly from the wall outlet, without going through the cable box. In most cases, these include the local affiliates of the big network channels, local government channels, and some other cable channels who have agreed to make their signals available unencrypted -- in my case, these are mostly home shopping networks, religious channels, and some foreign language channels.
The other channels (like ESPN, History, AMC, etc) typically are encrypted and require the cable box.
If you connect a coax RF signal splitter (available at Radio Shack and elsewhere), to the coax wire coming out of your wall, then you could connect TWO coax wires to the output side of the splitter, and then connect one wire to your TV (or alternatively to your Slingbox) directly, and the other to the input side of your cable box. The first coax wire would deliver the limited set of channels to whatever device it was attached to, and the other wire would go to the cable box, and the output from the cable box would contain the full suite of channels that your subscribe to.
Note also that many of those channels delivered directly from the wall may be in HD, so you could view them in HD on an HD-capable TV, for example.