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