Hi, welcome to Android Forums.
As I understand it, the IPhone uses Imessaging to send audio, video and picture files. Imessaging is sent using your mobile data or wifi connection and is the equivalent of MMS (multimedia messaging service).
Text messaging (SMS) uses a small amount of bandwidth within the communication channel between your cellphone and the network and is restricted to 160 text characters per message. This why even the most basic cellphone can send text messages.
To send audio, video or picture files you need to create an MMS message.
Hope this helps.