I want to ensure that people are listening to what I am saying, when they may occasionally get side tracked. I hear the term used on the phone regularly, but wonder if the term can be used with groups of people. Thanks.
With a large group of people, you could use 「もしもし」 in order to draw their attention. You would, however, need to know that that would be a rather humorous (and a bit unusual) way of using the phrase. I would at least not use it repeatedly with the same group.
With a single stranger or a small group of strangers, it is O.K. to use 「もしもし」 to mean "Excuse me!" You just need to know that this usage, though once just normal, has rapidly been becoming less and less common. It would often be a very old person using 「もしもし」 that way.
For the majority of present-day native speakers, the only place they say 「もしもし」 is on the phone.
In fact, the only one time someone has said 「もしもし」 to me on the street in the last several years has been by a foreigner who thought it just meant "hello".
Just to add. Saying もしもし to get someone's attention would generally considered quite rude (think saying "heeeloooo!" in English) however it could be used between friends when one is obviously day-dreaming etc.
It shouldn't be used to address a crowd.