Learn English – Is/Are “SAP Data Services” singular or plural

With compound antecedents connected by or or nor, make the pronoun agree with the nearer antecedent.

If one of the antecedents is singular and the other is plural, put the plural one last to avoid awkwardness.

--Hacker, Rules for Writers

I do believe that in both phrases you mention are grammatical and colloquially interchangeable.

However, I also think that there is actually a difference in the meaning. Peter Shor suggests this in his comment also. "Communications" and "Applications" refer to fields, or topic areas. So while "communication software" means something like "software that allows people to communicate with each other", "communications software" might mean something more like "software used in or made for the communications field". It's actually useful to use the plural here to disambiguate these two meanings. Notice that "Communications" is also plural in the title of the book - it's the name of a field or topic area.