How can I use a multiple concurrent transactions by the same client? For example:
method1() : T1
method2() : T2
method3() : T1
method4() : T2
A few SFSBs that handle UserTransaction objects is good idea?
You can suspend and resume transactions, but controlling transactions from a remote client won't work with the default transaction manager because it doesn't support transaction propagation. You can use a ditributed tx manager (Arjuna or Tyrex) or you can do it on the server side in a SFSB.