While a quick wiki/google flood me with numerous uml freeware, most of them doesn't meet my expectation (limited to "drawing" level instead of "modeling"). I know sparx's EA and IBM rational rose offers complete design-to-implementation toolkits but they are out of my budget :(
Would if be significantly different if I were to sketch using paper and pencil ?
Assume i know the full specification of UML, and aim to use it for
A good company shall use their money to buy you best tool in order to maximize your productivity. See rule 9 of The Joel Test
Honestly speaking, most of the time, I would think Marker Pen and White Board will be the best tool to communicate your idea between team members.