I have a new iPhone 4s, and my husband still has his 3gs. His phone will stay connected to the microcell.

I can force my 4s to connect, (by going into and out of airplane mode), but it won't stay connected. After a few minutes, it drops off.

I have turned off cellular data, rebooted both the phone and the microcell, and moved the microcell so it's directly in front of the window. It still won't stay connected to the microcell.

What else can I try?