Now that you mention it, ISTR the very same thing.
However, even with the MkII, some handfree kits worked without that resistor (probably because they had the resistor internally themselfs). My advice is to try wether the phone mute works without a resistor, and only if it doesn't, add the appropriate resistor.

cu,
sven
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proud owner of MkII 40GB & MkIIa 60GB both lit by God and HiJacked by Lord