In general, there is nothing wrong with displaying a infinite number of items in a carousel.
The problem arises by the nature of the data you want to display.
From "Designing Interfaces" p. 216 (Tidwell, 2011)
[Use when] Users will browse the items casually; they won't normally search for a specific item, or need to get an overall look at the entire list at once.
That means: if you simply display contacts as some kind of "overview" or something like a "suggested friends" feature - carousel is ok.
But if you expect the user to actually use the information, search it for specific contacts etc. then you'd rather choose a plain list or the thumbnail grid.
But the thumbnail grid can have a similar problem: if you show only pictures without info like the name of the contact, the user probably can't distinguish between the contacts (pictures might be showing more than one person etc..).
You could offer multiple views on your data. But keep in mind that this should only be done if all views have a good reason to exist. That means that a grid might be totally useless if you already have an ordinary "picture + info" list.
Also always consider to give the user the possibility to search through the collection.