spycatcher2k:
GPIO 4 is SDA
GPIO 5 is SCL2 seconds on GOOGLE : ESP8266-12 Pinout was all it took.
There is another, perhaps more up to date, point of view on this matter: ESP8266 Thing Hookup Guide - SparkFun Learn
It implies that one can indeed change the I2C pins:
Wire – The ESP8266 should work with any I2C sensor you can throw at it – just use the same Wire API calls you’re used to. There are a few differences:
Pin definition: The ESP2866 doesn’t actually have any hardware I2C pins – those labeled on the Thing are the default, but you can actually use any two pins as SDA and SCL. Calling Wire.begin() will assume pins 2 and 14 are SDA and SCL, but you can manually set them to any other pin by calling Wire.begin([SDA], [SCL]).