No, you could do it for as little as two analog phone lines. The trouble is that you do not get too goog quality, specially if the remote location (overseas) do not have good levels on the phone lines.
Also, the echo on the setup is increased when you use analog, two wire lines.
When you stay with T1 on one end and E1 on the other, you remain digital all the way, with only one encoding (when the call lives from your originating home into the first central office) and one decoding (when the call leaves the central office going into the remote phone)
I have done several test and you could do analog on one end and digital at the other without much quality loss.
Try to stay digital on the originating end (that way you get caller id and all the neat stuff) and you could go analog on the remote location.