Agreed. With no EQ the iPhone 4s doesn't sound warm to me at all. I consider the cMoy as not warm as well with the stock JDS opamps as a point of reference. Could the 4 vs 4s sound much different? 3rd party music apps?
Aka, expectation bias. It's amazing that an amp section that measures DEAD flat can sound warm.
I have the T1 here, and there's zero tonal difference between it and my iPhone 4.
Go have another listen.