I used it with a Treo from a few years back...entered and exited trades...wouldn't recommend but it worked in a pinch. More recently, I've used it with my iPhone. It works ok but very barebones. Just account balance, existing orders and executions. If I remember correctly, it can be quite involved (like 2-3 pages) just to select the futures, expiration and exchange.
I do have MobileTrader just in case my internet suddenly drops connection. My mobile phone uses a different connection than my home network. Hasn't happened to me yet (while trading that is), but the possibility of that happening is very real. Requirements for using MobileTrader are: Browser WAP 2.0 or higher Network Secure Web (internet port 443) Cookies not required (fully enabled or disabled)