The answer is really quite simple. The JAA PPL Theoretical knowledge requirement is given in Appendix 1 to JAR-FCL 1.130. As the PPL exams are produced nationally and not by the JAA, the RTF written exam was adopted as the PPL exam for Communications. It is one of the 7 written exams required for PPL issue. This is covered in LASORS Section C1.3 not Section B. App 1 to JAR-FCL 1.130 states:
Communication practical classroom testing may be conducted at the discretion of the Authority.
In the UK the Radiotelephony Licence is a National Licence not a JAA Licence (and is covered seperately in LASORS Section B) it requires a theory exam and a practical test. The theoretical exam is common to both licences but the RTF Practical is only required for the FRTOL.
If the training and testing for the two licences are conducted concurrently, you can take advantage of App 1 to JAR-FCl 1.130 Para 5 LASORS B1.2
5 Subject to any other conditions in JAR–FCL, an applicant shall be deemed to have successfully completed the theoretical examinations for the PPL(A) when awarded a pass in all parts within a period of 18 months, counted from the end of the calendar month when the applicant first attempted an examination. A pass in the theoretical knowledge examination will be accepted for the grant of the private pilot licence during the 24 months from the date of successfully completing the examinations.
So to put it simply, you do not have to take the RTF practical test as part of your JAA PPL however; it is highly recommended that you complete your FRTOL before you go off on solo navigation flights to reduce the workload if nothing else.