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 Ulucami's. 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.