Better to build one yourself, or buy one of the FTDI cables from their webshop and solder your own 2.5mm plug to it.
But beware of standard audio 2.5 plugs, they usually don't fit on motorola phones as their casing is too thick. Use plug and cable of a fitting headset or datacable.
Hint if you don't want to solder, find a usb to serial converter using a FTDI chip - a search for that shows mostly cable-less two-jack cased ones - and connect a standard serial T191 cable.
Regards, Mad