Perhaps you could try putting the jeans in the freezer overnight. The gum will be brittle and possibly easier to crumble and break off of the jeans.
For gum that is worked into your pants, Try to get as much gum off as you can with your hands or some tool that won’t damage your jeans. Heat up a little vinegar in the microwave. Take an old unwanted toothbrush and patiently scrub the excess gum off. It should come off easily.