A small additional circuit is required for Siemens M/S-35 series mobile phones. A circuit diagram can be found here. The biggest problem is to get a suitable plug, where all necessary contacts are available. On ebay there are unfortunately only adapters, which either lead out the audio lines OR provide a data communication with/without accumulator charging function… unfortunately not everything.
Mobile phone pin assignments can be found at Nobbi.com
The connection of a Sony-Ericsson P910i is a bit easier, here no interface with MAX3232 is necessary.
The cheap sound cards for partly 5€ are quite suitable for it. However, they often don’t have a stereo microphone input.
At the moment everything is in the absolute handicraft stage. It was tested with a Sony Ericsson P910i, but other devices like K610, 750 should work as well. A support for Siemens C35 etc. is in the works.
At the moment the device must react to the AT command „AT&FE0*ECAM=1″ with OK. Otherwise it will not work. For the support of further devices we need an AT command reference to the device of interest. If you have something corresponding and would like to make it available, please contact us.
AT command sets are currently being searched for: