Let me try and work it out I don’t think you will get an answer😉
imam MUST have joined a special network to receive calls also he must have a mobile phone purchased from some mobile shop somehow they have created a gateway to connect to the barzakh by dialling a special number.
Maybe imam has a landline where his followers ring but then that’s also questionable because where are the telephone lines reaching barzakh? Maybe leading to some deep underground cave?
A satellite phone? Maybe they have found a ripple in space where they can send a signal to barzakh.
Only thing I can think of is some telepathic powers where some how the connection connects to the imam in some Imami way by his closest followers and they use their own handset.
They must have the technology to bypass the barzakh,a doorway maybe where they can talk to the physical dead of this world.
I doubt it very much that you will get an honest answer in here or anywhere else, this is why the shia sect has become a joke.
I will leave it that and wait till some shia answers.