Banana phone

You call it the banana phone, and you think it's called the banana phone because it has a yellow cell phone cover.  I very strongly suspect that originally, back in the '80s, it was an actual "banana phone": that was the form factor of handheld cell phones back then.  They were about a foot long (or tall), with easily swappable external battery packs, and slight projections, at the top and bottom, housing the circuitry for the speakers and the microphone, since the technology has somewhat modified since then.

I strongly suspect that generations of emergency directors have passed the banana phone from one to another, along with the name, even as the phone itself has been upgraded, and the form factor has changed.  And that a yellow cell phone cover was added at some point ...

The banana phone is currently an iPhone.  And therein may lie a problem.  Currently we are using text messaging to alert the emergency team.  The iPhone does have provision for group texting, but you have already noted some limitations: that the iPhone will only allow eight numbers per group.  This means that we must use multiple groups.  But there is another, and more serious problem.

Text messaging is based on SMS, or short message service.  This is a standard protocol, and is common to pretty much all cell phones.  Unfortunately, that is not what iPhone uses when it creates groups.  When it creates groups, all messages, regardless of type, are sent as MMS messages, MMS standing for multimedia service.  This is the service that allows for audio messages, video messages, pictures, and other types of media aside from just straight text.  Unfortunately, the protocol for MMS is not fully agreed to by all cell phone manufacturers, or cellular providers.  And, specifically, Apple uses some quirks of its own in the MMS protocol.  Therefore, any messages sent from an iPhone, when being received on a non-iPhone, may result in some oddities.

Sometimes the message simply isn't received at all.  In other cases, the receiver may receive a message saying that a mixed media message is about to arrive, except that the message never actually does arrive.  In any case, it is often problematic, and therefore it is an unreliable way to send messages to a large group of people, with different types of cellular equipment and service.