That's not what i mean.
Here is an example of a picture with a timestamp:
Aha, you want an "in-band" timestamp printed
on the photo. Most people prefer the modern "out-of-band" timestamps saved in the EXIF data so as not to take away from the actual picture contents.
So exactly where do you want the timestamp to be seen? If you'd be satisfied with having it when viewing the photos on the PC, you could use Irfanview to add them after transferring your photos to the PC, see here:http://en.irfanview-forum.de/vb/showthread.php?416-Printing-timestamp
If, however, you want the timestamps to be seen on your phone (and being able to bring them up in the picture details doesn't satisfy you), that's a bit harder. Maybe there's an app in the Android market for this already, but I couldn't find one in a quick search. I suppose it wouldn't be too hard to develop yourself, if you have some programming skills...