The myTouch Slide is expected to have Android 2.1 out of the box with an Arm11 based processor running at 600MHz (like the new Qualcomm MSM7227 seen on the HTC Legend). The device is said to have a 1300 mAh battery, camera of unknown MP with LED flash, slide out 4 row physical QWERTY keyboard, optical trackpad, a display with resolution of 320 x 480 and a microSD slot that can be reached without having to take out the battery. These aren't what you would call the specs of a superphone so it looks like it will be another middle of the road audience that T-Mobile will be aiming for with this phone.
T-Mobile myTouch Slide Preliminary Specifications
source: FCC via AndroidandMe