Abdullah ibn Umar didn't see a problem with calling upon the dead either in the narration Abdur Rahman ibn Sa’d narrates Ibn Umar (radhiyallahu 'anhum) had numbness in his leg, whereupon a man said to him, "Remember the most beloved of people to you", so he said, "Ya Muhammad". [Imam al Bukhari, Kitab ul Adab ul Mufrad, Hadith 964]