One big problem with "There is a couple, while they lean against the wall, gaze longingly into each other's eyes." is that "couple" is not the subject of the sentence. It's even debateable whether there is one. In order to be correct, this sentence would have to be:

The couple, while they lean against the wall, gaze longingly into each other's eyes.

or

There is a couple, leaning against the wall, gazing longingly into each other's eyes.

I also agree that a collective acts as a singular when it refers to one unit:

The couple is sitting in the park talking.

and that it is plural when they are individual:

There are a couple of people in the park.

I would like to suggest that, because they are possibly receiving calls continuously, that is, they are currently receiving your call, and have quite possibly already received calls, hence the necessity for this message, that a possible construction might be:

Calls will be answered in the order they are received.

or alternately:

Calls are answered in the order they are received.

The first implies that calls are not currently being answered, perhaps because the business is closed, while the second implies that they are diligently working on a continuous backlog.

The issue of ambiguity is not entirely warranted. When speaking, people usually measure their metre to indicate the meaning they intend, and punctuation serves this purpose in writing.