Regarding the use of non-BMW starTAC phones, it appears that you must use the BMW phone. I did try using my none BMW 7000series TDMA phone after installation of a BMW phone and it could not be programmed to work in the M5. Also of interest is an accessory part seldem if ever mentioned. The BMW phone can be installed with a RF amplifier, called a "compensator" in BMW speak, to make up for the signal loss in the coax lead to the external antenna. The BMW part # is 84 11 0 009 117 and an installation kit # 84 11 0 017 787. Cost of the amp and installation kit run abour $300 above the standard phone. The compensator had never been seen at my dealership before I ordered it.