Type I:

Identical to type II, except requires extra cables for connectors like the RJ-11 and RJ-45. However, offers more flexibility to where it can be placed in the computer.

Type II:

Used when size is not important. Type II can integrate the RJ-11 and RJ-45 connectors and did away with extra cables.

Type III:

SO-DIMM style connector that can be installed with a mere 5 mm overall height above the system board. Cabling to the I/O connectors also allow type III cards to be placed anywhere in the system.