While both are SIP client APIs there are differences in the two, implementing JAIN SIP on Android SIP APIs will be difficult or at best incomplete because JAIN SIP is a much lower level API.
For example Android SIP APIs do not expose the SIP Stack as you would expect in JAIN SIP, you cannot access SIP transactions in Android etc.
With Android API you can create a manage a SIP client easily and that is what it is ideally suited for without going to low level SIP protocol tinkering.
If you want to implement JAIN SIP API layer in Android you may have to write or use your own SIP stack (like the NIST JAIN client).