ما سمعت صوت الرسالة لاني كنت لابس سماعات.

It is Levantine colloquial Arabic.

A few clues:

• ما سمعت for I didn’t hear is a common colloquial negation pattern.
• كنت لابس is very conversational and typical of spoken Arabic.
• لاني is an informal spelling of لأني / لإني in speech.
• The whole sentence sounds natural in everyday spoken Levantine, not formal written Arabic.

A more formal Standard Arabic version would be something like:

• لم أسمع صوت الرسالة لأنني كنت أرتدي سماعات.

Because ما is a very common way to negate past-tense verbs in Levantine.

So:

• سمعت = I heard
• ما سمعت = I didn’t hear

This is much more natural in everyday speech than using formal negation like لم أسمع.

A useful pattern is:

• ما + past verb

Examples:

• ما عرفت = I didn’t know / I couldn’t tell
• ما فهمت = I didn’t understand
• ما شفت = I didn’t see