Differential Amplifier Input Line-Level Signaling
Since Io is a current source the emitters of the transistors will actually be at approximately -0.7V so the transistors will be in their active region.

If the emitter resistors are too low however the amplifier will saturate if the signal goes to high or too low though. Normally this type of stage is used where Vi2 is derived from the output of the following amplifier and provides negative feedback.