N900 Hardware Bus I2c
Hardware
/sys/bus/i2c/drivers# ls -d */*-* ad5820/3-000c dummy/1-004a radio-si4713/2-0063 adp1653/2-0030 dummy/1-004b smia-sensor/2-0010 aic34b_dummy/2-0019 et8ek8/3-003e tpa6130a2/2-0060 aic3x I2C Codec/2-0018 lis302dl/3-001d tsl2563/2-0029 dummy/1-0049 lp5523/2-0032 twl4030/1-0048
Software
The n900 software driving I2C comes in three flavours.
Firstly, there are a large number of kernel drivers.
Then, there are a small number of devices 'bit banged' through I2C ioctls - BME for example does this.
Finally, there are probably some I2C components in the Rapuyama and assorted cellphone/GPS hardware. These are not visible to the casual developer. (you have to open the n900 and probe stuff, or hack the phone firmware).