The i.MX28 CPU I2C pins are not exposed to any external interfaces on this SBC. Because of this, bitbanging is strongly recommended for any attached peripherals that would utilize I2C.
Technologic Systems recommends using direct bitbanging of I2C pins from userspace to drive an I2C interface. See the DIO section for further information on manipulating DIO pins.
Another option is to implement i2c-gpio in linux. This allows for an I2C physical interface on GPIO pins, but uses the kernel I2C software interface to read and write data on the I2C bus. See linux kernel documentation and i2c-dev for more information on this.