It's interesting that God spoke directly to Abimelech through a dream in Genesis 20. He didn't speak through a prophet, and the dream required no interpreter. It was just God and a Philistine king. The following text indicates that Abraham and Abimelech had a great deal of respect for each other.

I wonder if the Philistines weren't so bad at first and, like the Israelites, were corrupted by their Canaanite neighbors. Based on Philistine graveyards, archaeologists say that their genetic makeup changed dramatically (more Mediterranean) sometime after this point, and then slowly drifted back to what it was before (more Canaanite).