The verb oír involves an auditive passive perception, while escuchar suggests an active perception. In other words, if we do not pay attention, we hear (oímos), but we do not listen (no escuchamos).
So, we can listen (escuchamos) to music, the radio, a friend... You must not use any preposition with escuchar:
Escucho ___ la radio todas las mañanas = I listen to the radio every morning
Escucho ___ música mientras trabajo = I listen to music while working
When speaking of people, if we think that they do not pay attention to us, we ask:
¿Me estás escuchando? = Are you listening?
If we expect no message, we just hear (oímos). Oímos el viento (the wind), los ruidos (noise), los pasos (footsteps), a los vecinos (neighbors)...
Normally we hear unintentionally, like in
Todas las noches oigo las conversaciones de mis vecinos que no me dejan dormir = Every night I hear the conversations of my neighbors who don’t let me sleep
Also we use oír to indicate that the message is received:
Te oigo muy mal = I hear you very bad
In Latin America, sometimes in Spain, some people confuse these two verbs using escuchar instead of oír, but it is a mistake:
CORRECTO: No te oigo – I can not hear you
INCORRECTO: No te *escucho= I’m not listening to you
Like in English we can use oír with an infinitive:
No te oí entrar = I didn’t hear you come in