Comma + if

Make a phone call, if the service is available.

I think it is better to have the comman in your sentence.  Usually a comma will not make a difference in the meaning of a sentence.  It just provides a convenient and natural place for a reader to take a little pause.  It makes the sentence flow better and easier to understand.

Make a phone call, if the service is available.

This is  a conditional sentence, which is another way of saying it is a complex sentence.

Complex sentences have the form:
Conjunction x, y OR y conjunction x
"If" here is the conjunction.

The correct punctuation, therefore, would be:
If the service is available, make a phone call (with a comma); or
Make a phone call if the service is available (without a comma.)

Hi,

When two simples sentences are joined together using a conjunction, it should be preceded by a comma. This seems a little dogmatic to me. For example, when  both sentences are very short, I don't see that a comma is always necessary or desirable.

eg I love you and you love me.

I called you but you didn't answer the phone.

Best wishes, Clive

Hi,

So is it the case of grammar rules changing and evolving over time?  Yes, I think there's a lot of truth in what you say here. Both language and its grammar do evolve. I think one example is sentence length. Generally speaking, today we favour simpler sentences, and I think the result is that the use of commas is reduced and simplified. These are generalizations, of course.

Or should one consider the source carefully when referencing these material? Well, you should always think about that. However, I don't mean to denigrate rules and the people who write about them, who I'm sure know a great deal more about technical grammar than I ever will.  Rules are very important and useful, particularly for English learners. But they're just rules, and should not be written as dogma.

Best wishes, Clive