Cordless Phones

Hi there,
This is a very specific question, but I might get some help.
I need 2-3 cordless phones for a shop which has an outdoor area that needs a 300 metre range. The port will be in the shop and the range will be for outdoors.
I need durable phones as they will be outside.

Any help would be greatly appreciated

The BT Diverse Elements phones sound ideal here. Weatherproof and up to 1km range. BT just re-badge other manufacturer's tech, so I'm sure other brands do similar models.