I have the P32 (roughly same size as the P3AT) and I have the P11.
No, the P11 is not easily concealed in the pocket. I got a FOBUS holster for it, for my hip, and it's outstanding. The rig and gun are so light, you barely know it's there, and it's very secure. Easy to deploy as well. Very comfortable.
The P11 is easily concealable under a loose shirt too, summer or winter.
hope this helps.
And, btw, I don't care what anyone else here says about reliability - the P11 is very reliable and accurate - despite the heavy trigger pull.