این دو تا تفاوتی از لحاظ پیاده سازی با همدیگه ندارن ولی ویکیپدیا یه تفاوتش رو اینطوری گفته بود:
I²C is the basis for the
ACCESS.bus, the
VESA Display Data Channel (DDC) interface, the
System Management Bus (SMBus),
Power Management Bus (PMBus)and the Intelligent Platform Management Bus (IPMB, one of the protocols of
IPMI). These implementations have differences in voltage and clock frequency ranges, and may have
interrupt lines.
TWI (Two Wire Interface) or TWSI (Two-Wire Serial Interface)
is essentially the same bus implemented on various system-on-chip processors from Atmel and other vendors.
[6] Vendors use the name TWI, even though I²C is not a registered trademark. Trademark protection only exists for the respective logo (See upper right corner) and patents on I²C have now lapsed
این طور که من برداشت کردم احتمالا فقط محصولات اتمل از I2C به این اسم استفاده می کنن.