Husk corn, discard husks and silks, and rinse ears. With a sharp knife, cut corn kernels from cobs into a bowl.
In a 5- to 6-quart pan over medium-high heat, frequently stir pancetta until lightly browned and crisp, 5 to 7 minutes. With a slotted spoon, transfer pancetta to towels to drain.
Add onions to pan; stir frequently until they're just beginning to brown, 3 to 5 minutes. Add corn, potatoes, peppers, broth, and oregano. Bring to a boil over high heat, stirring often. Reduce heat, cover, and simmer, stirring occasionally, until potatoes mash easily when pressed, about 15 minutes. Discard oregano sprigs.
In a blender, whirl about 1/3 of the soup mixture (use a towel to hold down blender lid) until smooth. Pour purée back into pan with remaining soup. Add cream and stir until soup is hot, about 1 minute. Add salt and pepper to taste.
Ladle the soup into bowls; top equally with cooked pancetta.