Learn Hardcore Icelandic: Síminn hringir núna.

Icelandic puts the definite article at the end of the noun. The base noun is sími (phone). To say “the phone,” you add the suffixed article -inn (masculine nom. sg.): sími + inn → síminn. So Síminn hringir núna literally reads “Phone-the rings now.”

Can I say Sími hringir núna without the article?

It’s grammatical but odd in most contexts. English “A phone is ringing now” is already unusual; in Icelandic you normally mean a specific, known phone, so you use the definite: Síminn hringir (núna).

What’s the verb’s base form and how is it conjugated in the present?

The infinitive is að hringja (“to ring; to call”). Present tense:

ég hringi (I ring)
þú hringir
hann/hún/það hringir
við hringjum
þið hringið
þeir/þær/þau hringja

English says “is ringing.” Why is Icelandic using simple present hringir?

Icelandic often uses simple present for actions happening right now. Síminn hringir (núna) naturally means “The phone is ringing (now).” You can also use the progressive-like construction Síminn er að hringja (núna), which focuses on the ongoing process. Both are fine; simple present is very common.

Is Síminn er hringjandi a good translation of “is ringing”?

No. Present participle as a progressive (… -andi) is not used like in English. Use hringir or er að hringja instead.

What’s the difference between hringja by itself and hringja í + accusative?

hringja (intransitive): the device (or a bell) rings. Example: Síminn hringir.
hringja í e-n/e-ð (transitive with preposition í + acc.): to call someone/something. Example: Hann hringir í mig (“He calls me”).
So Síminn hringir í mig would mean “The phone is calling me,” which isn’t what you usually want.

Why not símann or símanum here?

Those are other cases of the definite noun:

síminn = nominative (subject) → needed here
símann = accusative (direct object): Ég heyri símann hringja (“I hear the phone ring”)
símanum = dative: Það er hringt í símanum can mean “There is ringing on the phone” (more technical/locational)
símans = genitive (possession): hljóðið símans (“the phone’s sound”)

Do I need núna? What’s the difference between núna and nú?

You don’t need it; Síminn hringir already implies “now” in context. núna means “now (at this moment)” and is very common in speech. nú can also mean “now,” but it’s shorter, sometimes more formal, and also used as a discourse word (“well/now”).

Can I move núna to the front?

Yes. Núna hringir síminn is fine and puts extra emphasis on “now.”
Neutral: Síminn hringir núna.
Fronted/focused: Núna hringir síminn.

How do I say “My phone is ringing now”?

Use a postposed possessive (typical in Icelandic): Síminn minn hringir núna.
You can also say: Síminn minn er að hringja núna.

Is it okay to drop the subject and just say Hringir (núna)?

As a full sentence, Icelandic normally keeps the subject. But as an exclamation, people do say Hringir! (“It’s ringing!”) when the context is obvious.

Any quick pronunciation tips for the whole sentence?

Síminn: first syllable stressed; í is long like “ee”; final -nn is a doubled n. Roughly “SEE-minn.”
hringir: initial hr- is like an “r” pronounced without voice (a whispery r); ng as in English “sing”; final -ir like “-ir” in “mirror” (but shorter). Roughly “H’RIN-gir.”
núna: ú like “oo” in “soon”; stress on the first syllable. Roughly “NOO-na.”

Could Síminn be a company name here?

Context decides. Síminn (capitalized) is also the name of an Icelandic telecom company. In everyday speech, though, síminn with article usually just means “the phone,” especially with hringir. If you meant the company calling you, you’d typically say Síminn er að hringja í mig (“Síminn is calling me”).