I recently purchased an AT&T 3G Microcell and spent much time troubleshooting with AT&T. I started to suspect my SA 520W and moved the Microcell to an old PIX 501 on my secondary DSL line. It worked perfectly on the PIX 501.
I've been unable to discern any workable configuration on the SA 520W to allow the AT&T/Cisco 3G Microcell to function properly.
Thanks in advance.