Learn Hardcore Finnish: Soitan sinulle huomenna aamulla.

Finnish doesn’t have a dedicated future tense. It commonly uses the present tense together with a time expression like huomenna (tomorrow) to indicate future time. So soitan literally is I call / I will call, and huomenna aamulla makes it clearly future.

What is the base form (dictionary form) of soitan, and how is it conjugated?

The dictionary form is soittaa (to call / to ring / to play). Conjugation here:

soita- (verb stem)
-n = 1st person singular ending
So soitan = I call / I will call.

Why does it say sinulle and not sinua?

Because soittaa takes different case patterns depending on meaning:

soittaa jollekin (allative: to someone) = to call / to phone someone → soitan sinulle
soittaa jotakin (often partitive: something) = to play (music/an instrument piece) → e.g. soitan pianoa (I play the piano), soitan kappaletta (I play a piece)

So for “call you (on the phone)”, Finnish uses sinulle (allative).

What case is sinulle, and what does it literally mean?

Sinulle is the allative case of sinä (you, singular).
Allative often corresponds to to / onto in English. Here it’s “to you” in the sense of placing the call to you: I’ll call you.

What case is aamulla, and why is it used?

Aamulla is aamu (morning) in the adessive case (-lla/-llä).
With times of day, the adessive is commonly used to mean in the morning / in the evening / at night, etc.:

aamulla = in the morning
illalla = in the evening
yöllä = at night

Could I say huomenna aamuna instead of huomenna aamulla?

Usually you say huomenna aamulla.
Aamuna (essive) can exist, but it’s less natural for “tomorrow morning” in ordinary scheduling/when-you’ll-call contexts. The standard everyday choice is huomenna aamulla.

Is the word order fixed, or can it change?

It can change. Finnish word order is fairly flexible, and changes often reflect emphasis or what is “known vs new” information. These are all possible with slightly different emphasis:

Soitan sinulle huomenna aamulla. (neutral)
Huomenna aamulla soitan sinulle. (emphasizes the time)
Sinulle soitan huomenna aamulla. (emphasizes that it’s you, not someone else)

Can the pronoun sinulle be omitted?

Yes, if it’s clear from context whom you mean:

Soitan huomenna aamulla. = I’ll call tomorrow morning.
Finnish often drops pronouns/objects when they are understood.

Does soittaa definitely mean “call” here? I thought it can mean “play (an instrument)” too.

By itself, soittaa is ambiguous: it can mean call/ring or play.
In this sentence, sinulle strongly signals the “call (phone)” meaning, because soittaa jollekin is the standard structure for calling someone. If it were “play,” you’d typically have a musical object instead (e.g. soitan kitaraa).

How would this change for polite/plural you?

Use te-forms:

Soitan teille huomenna aamulla. = I’ll call you (plural/polite) tomorrow morning.
Here teille is allative of te (you, plural/polite).

What’s the pronunciation of Soitan sinulle huomenna aamulla?

Key points:

Finnish stress is usually on the first syllable: SOI-tan SI-nul-le HUo-men-na AA-mul-la.
Double letters are held longer: -ll- in aamulla is a longer l sound than a single l.
oi in soitan is a diphthong (roughly like oy in boy).
huo in huomenna is a smooth sequence; don’t insert an English-style w.