Configured Android phones with the simple Username/Password pointed to a specified server address:5061 and selected TLS, turned on the proper codecs. However, when trying the same configuration on an iPhone it pops a "Service Unavailable" which I am assuming is due to a signaling error as I cannot select TLS anywhere. The Transport Protocol options on the iPhone are TCP or UDP, am I missing something?

Please confirm whether calls can be placed only to phones that have an account on the same SIP service