Much appreciated!!

Sorry I could not answer your call earlier.

I was at a meeting/course.

Was it important?

Telefonunu açamamamý için kusura bakma.

Toplantýdaydým./Kurstaydým.

Önemli miydi?

Please wait for corrections.

Sorry, on second thought I think this one should be:

Telefonunu açamamak için kusura bakma.

 I don´t think açamamak or açamak are words, in your first attempt it appeared you were attemptiýng a negative potential verbal noun.  "açamamam"  not able to be openýng or swýtchýng on the (phone).  I would have wrýtten

"açmadým".  All that said 

"Telefonunu açamamak için kusura bakma" means  "your telephone (call) not answerýng don´t be borrowed" I guess that works. IMHO

Thank you Uzun. What I was thinking here is that için is a postposition with absolute as it´s object, so it would need - mek noun/verb. But maybe I´m wrong. Maybe it´d be better to say something like:  "Telefonunu açamadýðýmý için kusura bakma" or "Telefonunu açamadýðýmden için kusura bakma".

Would a native speaker or someone more experienced will be kind enough to explain:

- if there´s a difference in meaning between - mek için and -diði için?, and

- with kusura bakma, when you want to say you´re sorry for something, what would be the correct way to do so?

Thank you in advance.

afedersin telefonu´na cevap veremedigim icin.

ben toplanti´da,kurs´daydim.

onemli´miydi?

So it looks like the -diði için is the winner in this sentence structure.

Would it work with kusura bakma? That is, would the sentence: "Telefonunu açamadýðým için kusura bakma". or "Telefonuna cevap veremediðim için kusura bakma". be correct as well? Would kusura bakma be used in this context at all?

Thanks.

´ sign is used only after private names.

you don´t need to use it after ordinary nouns like telefon, kurs, etc.

telefonuna

toplantýda

kurstaydým

önemli miydi

it is either telefonunu açmadýðým/cevaplamadýðým/yanýtlamadýðým için kusura bakma.

or

telefonunu açmamam/cevaplamam/yanýtlamam için kusura bakma.

but actually first one is better, because you can understand that it happened in the past, but second is for a more general habit.

for "could", of course you add an "a":

and i forget some "ma" s in first post

i want modify function back!