I've used the first two smart phone apps in a pinch:

1) PocketCloud -- which allows me to remote into any of my servers. Obviously, the screen size and keyboard are not ideal, but it can be done. There are Mac or Windows desktop with your iPad, iPhone or iPod Touch versions. (See: http://itunes.apple.com/us/app/pocketcloud-remote-desktop/id326512817?mt=8 )

2) SQL Wrenches -- which allows me to execute stored procedures & views on any server. It can be used to monitor disk space, backups, etc., anything you can do with a view or stored procedure. However, I have noticed that the more joins in my logic, the more likely the app is to time out before it returns results, even if the result set is small. This app has potential, but it's not quite there yet.

(See: http://itunes.apple.com/us/app/sql-wrenches/id426888582?mt=8 )

3) SQL Guages -- which provides various PerfMon like measurements. (See: http://itunes.apple.com/us/app/sql-gauges/id404189907?mt=8 )