Hi Dao,
This is very common question.
In SMP3.0 , there is not a direct way to connect to BAPI/RFC since SMP3.0 is based on OData protocol. You have to use SAP NWG to expose OData service to connect to smp3.0.
If you have backend other than SAP like DB2, SQL, web services then you have to use " Integration Gateway" to convert into ODATA services.
NOTE: SMP3.0 mobile sdk doesn't have any kind of workspace like we have till SMP 2.3.X where we can directly connect to SAP system using BAPIs.
Rgrds,
Jitendra