Android phones running Android OS 2.2 (Froyo) or newer have a built-in tethering feature. Tethering lets you share an Android phone’s 3G or 4G wireless data service with another device over a USB cable, Bluetooth or WiFi. This is extremely useful if you have a WiFi-only tablet or notebook. However, phones running older versions of Android do not have this feature. And, carriers have been requiring payment for tethering service. The workaround to these problems is to use a third party app that provides tethering. ThisIsMyNext’s Chris Ziegler (formerly of Engadget) notes that:
I verified this on a Verizon labeled Motorola Droid. The free and paid versions of PdaNet do not show up in search results in the Android Market on the device. This is the case even though my Droid does not have Verizon service anymore and is being used as a WiFi-only device. However, PdaNet is visible and downloadable on my unbranded and unlocked Nexus One (also currently a WiFi-only device).
It should still be possible to sideload apps like PdaNet if the carrier and vendor have not locked down this capability in your Android phone.