El tono de llamada suena antes del buzón de voz.

Yes. Tono de llamada is the standard way to say ringtone.

• tono = tone
• llamada = call

So literally it is call tone, but in natural English that corresponds to ringtone.

In everyday Spanish, people may also just say tono if the context is clear.

Both, depending on context.

The verb sonar means to sound or to ring. In phone-related contexts, suena is often best understood as rings.

So in this sentence, El tono de llamada suena means something like:

• The ringtone sounds
• or more naturally, The phone rings / the ringtone plays

Spanish often uses sonar where English would prefer ring.

Because sonar is a stem-changing verb.

In the present tense, the o changes to ue in most forms:

• yo sueno
• tú suenas
• él/ella suena
• nosotros sonamos
• vosotros sonáis
• ellos suenan

So suena is the correct he/she/it form.

Spanish usually needs an article where English might not.

So el tono de llamada sounds natural, while leaving out el would sound incomplete in normal Spanish.

This is very common:

• El teléfono suena
• La puerta está abierta
• El coche no arranca

Spanish generally likes definite articles with nouns when talking about a specific thing or a thing in general context.

Because de + el contracts to del.

So:

• antes de + el buzón de voz
  becomes
• antes del buzón de voz

This contraction is mandatory in normal Spanish.

Compare:

• al = a + el
• del = de + el

Literally, it means voice mailbox:

• buzón = mailbox / box
• voz = voice

But the normal English equivalent is voicemail.

So although the literal parts are useful to understand, you should think of buzón de voz as the Spanish expression for voicemail.

In Spanish, de is very often used to link nouns together, where English might use:

• of
• a noun used like an adjective
• or a compound noun

Examples:

• tono de llamada = ringtone
• buzón de voz = voicemail
• tarjeta de crédito = credit card
• mesa de madera = wooden table

So de does not always translate word-for-word as of. It often just helps build compound noun phrases.

It is understandable, but it sounds a bit technical or literal.

A more natural everyday Spanish phrasing might be:

• El teléfono suena antes de que salte el buzón de voz.
• Suena antes de que entre el buzón de voz.

In Spain, people often say salta el buzón de voz for the voicemail picks up / kicks in.

So your original sentence is fine in a technical or explanatory context, but in conversation many speakers would choose a structure with antes de que....

Spanish often uses the present tense for general facts, instructions, settings, and descriptions.

So suena here can describe what normally happens:

• the ringtone rings first
• then voicemail comes later

It does not have to mean it is happening right this second. It can simply describe the usual sequence.

Because the sentence is talking about the general feature or system as one thing:

• one ringtone
• one voicemail service

Spanish often uses the singular for this kind of general statement.

For example:

• El correo llega tarde.
• La música suena bien.
• El buzón de voz no responde.

If you were talking about multiple ringtones or multiple voicemail boxes, then you would use the plural.

Sometimes, yes, but they are not always exactly the same.

In Spain:

• buzón de voz usually means voicemail
• contestador can mean answering machine

In everyday speech, people may use contestador quite naturally, especially in older or less technical contexts. But if you specifically mean mobile/network voicemail, buzón de voz is very common and precise.

Because Spanish often leaves that kind of ownership unstated when the context already makes it obvious.

If you are talking about phone settings or how a call works, el buzón de voz is enough.

Adding possession is possible, but only if needed:

• tu buzón de voz = your voicemail
• el buzón de voz del teléfono = the phone’s voicemail

Without that extra detail, the sentence sounds more general and neutral.

A few useful points:

• llamada: in most of Spain, ll is pronounced like y in modern speech, so roughly ya-MA-da
• buzón: the z in Spain is pronounced like the th in think, so roughly boo-THON
• voz: again that Spain z sound, roughly both

So a rough Spain-style pronunciation guide would be:

el TO-no de ya-MA-da SWE-na AN-tes del boo-THON de both

That is only an approximation, but it helps with the main sounds.