The dual-axis gyro IDG-2000 will be released in October and is 4x4x0.9mm, so about the same size of the thinnest 3-axis accelerometer (the volume ratio is 1.28). I don't know the OEM price. The IDG-1215 was $20 per unit (but per thousands, the price should be much lower). So, I don't think it would really be expensive.
Smartphones are not just phones. They have cameras. And it has been said that gyros help image stabilization.