Mpango ukibadilika, nitakupigia simu.

It breaks down like this:

• u- = subject agreement for mpango
• -ki- = if / when
• badilika = change, become changed

So ukibadilika means if it changes or when it changes, referring to mpango.

In the full sentence, that gives:

• Mpango ukibadilika = If the plan changes

Good question, because u- can indeed mean you in other contexts.

Here, though, u- is not you. It is the subject marker that agrees with mpango.

That happens because Swahili uses noun classes, and mpango belongs to a class that takes u- for singular subject agreement.

So:

• mpango umebadilika = the plan has changed
• mpango ukibadilika = if the plan changes

If the verb really meant you change, the context would be different, because there would not be mpango right before it as the subject.

-ki- often marks a condition or a time relationship. Depending on context, it can mean:

• if
• when
• sometimes whenever

In this sentence, if is the most natural translation:

• Mpango ukibadilika, nitakupigia simu.
• If the plan changes, I’ll call you.

But the same form can sometimes feel close to when, especially when the speaker thinks the thing is a real possibility.

Because these two verbs are related but not the same:

• kubadilika = to change, to become different
• kubadilisha = to change something

So:

• Mpango ukibadilika = If the plan changes
• Nikibadilisha mpango = If I change the plan

In your sentence, the plan is the thing undergoing the change, so kubadilika is the right choice.

It can be broken down like this:

• ni- = I
• -ta- = future marker, will
• -ku- = you
• -pigia = call / ring for, call to

So:

• nitakupigia = I will call you

Then simu is added:

• nitakupigia simu = I will call you on the phone

Yes, piga has several meanings, and its basic sense is often something like hit / strike. But in Swahili, many common expressions use piga idiomatically.

For phone calls:

• kupiga simu = to make a phone call
• kupigia mtu simu = to call someone

So even though the verb may look strange literally, this is a normal everyday way to say call in Swahili.

A useful contrast:

• kuita = call out / summon / name
• kupigia simu = call on the phone

Because the idea of if is already built into the verb through -ki-.

So Swahili can express the condition just by saying:

• Mpango ukibadilika... = If the plan changes...

You can sometimes use kama in conditional sentences, but here it is not necessary. The sentence sounds natural without it because -ki- already does that job.

The version with the condition first is very natural:

• Mpango ukibadilika, nitakupigia simu.

This is similar to English If the plan changes, I’ll call you.

In conversation, Swahili can sometimes place the condition later, but putting it first makes the sentence especially clear and natural. So for learners, the given order is a very good model to follow.

Then the noun class agreement would change.

• mpango = plan
• mipango = plans

With mipango, the verb would use i- instead of u-:

• Mipango ikibadilika, nitakupigia simu.
• If the plans change, I’ll call you.

So this is a good example of how Swahili agreement changes with the noun class.

Then the object marker for you would change.

• nitakupigia simu = I will call you (one person)
• nitawapigia simu = I will call you (more than one person)

So the full sentence would be:

• Mpango ukibadilika, nitawapigia simu.
• If the plan changes, I’ll call you all.

This is a very common kind of change in Swahili: the verb shows who is being acted on.