A SIP is an input mechanism for the Pocket PC. These are things like the virtual keyboard and handwriting recognizer you can select in the lower right corner of the Pocket PC screen. Anywhere WX includes its own custom SIP which provides "big" buttons for entering text while flying. This is adequate for entering small amounts of text (e.g. waypoints, airports), but can get a little tricky for e-mail, especially during single pilot operations.
For e-mail in particular, I found that I had three basic needs which current input mechanisms lacked:
AMSIP is a simple SIP which provides a set of configurable "macros". These macros are nothing more than canned text the user has configured ahead of time. These can be e-mail addresses, short messages, etc. None of this is Airmail specific and could be used for any application (as can Anywhere's custom SIP). In fact, one could even store commonly used waypoints for entry into other Anywhere WX applications.
AMSIP also includes a small set of "macro substitutions" which can do things like insert the current lat/long as extracted from Anywhere WX. These features are Anywhere WX specific but have a sensible default behavior if you try to use them when Anywhere WX isn't running.
AMSIP is easy to install, use, configure, or uninstall. AMSIP has been verified to work with version 1.52 of Anywhere WX running on the iPAQ 2210 with the SatPackII integrated GPS. I don't have access to other hardware, but I see no reason why AMSIP wouldn't work with other Anywhere WX supported platforms.