Indefinite article - He tenido carta de Alan

Indefinite article - He tenido carta de Alan
 

He tenido carta de Alan. - De eso quiero hablarte.

Is it correct to omit the indefinite article before 'carta' here?

I would have always written this sentence using the article:
- He tenido una carta de Alan. - De eso quiero hablarte.

Many thanks in advance.

The article is often dropped. I cannot point out when people do that, but if you use the article all the time, it's correct. :)