Hi yes in some sources it said they were used as friday mosques some are not named Ulucami but they are the largest and most times oldest mosques of a city They have no difference in function with the other Ulucamis For example Alaeddin Mosque in Konya is not called Ulucami but it has the function of a Ulucami in the city of Konya It is the biggest mosque and probably oldest Same is the case in the Isa Bey Mosque