the ggsn 30 and a corresponding pdp context response message sent in step s 525 acknowledges back to the user 4 the establishment of this primary pdp context from the ggsn 30 once the user has got ip connectivity the user may access the ims by registering therein to this end the method provides for a step of receiving a sip register message in step s 530 at the p cscf and a step of forwarding the sip register message in step s 535 towards further ims infrastructure 9 in this respect the well known 3gpp ims registration procedure as explained above for background of the present invention takes place the ims infrastructure 9 thus represents all the ims entities referred therein such as i cscf hss and s cscf other than the p cscf in order to carry out these steps of receiving and forwarding the sip register message and as illustrated in fig1 the p cscf is equipped with a protocol handler 16 which is in charge of managing the sip messages s 50 between the user 4 and the other ims infrastructure 9 in particular this protocol handler may include dedicated means 15 to deal with pure sip messages and protocol at this stage different alternative embodiments are possible to accomplish objects of the invention in one embodiment not drawn in any drawing the p cscf waits for the reception of a sip u201c 200 ok u201d message from the ims infrastructure indicating the successful registration of the user 4 in ims before triggering the next actions in another embodiment illustrated in fig3 a the p.