It depends on your device. Some Android phones support a headset input through the headphone jack (such as through this device [Traveler Guitar MI-10]). In that case, a simple adapter can allow you to feed an audio line in.
Other devices allow what is called host support for USB. If this is the case, then you may be able to use a USB audio interface if it has driver support for Android (not sure if there are any such products yet) (Update: There appears to have been some success here. [USB Audio Recorder Pro App] )
A third option that should be more universal would be to look for a bluetooth device that can take a line input and feed it in to whatever software you are using in Android. Exact support would depend on the profiles your device supports, but something like this [Britelink Bluetooth Audio Transmitter] could possibly work.
It would also be important to check the documentation of whatever software you want to use on Android since the devices supported by a particular application may not include all options.