On the Mac, you can use an NSAttributedString to remove html tags, like
NSString *htmlStr = @"Foo <img src=\"
http://www.site.com'\" /> Bar.";
NSData *data = [htmlStr dataUsingEncoding:NSUTF8StringEncoding];
NSAttributedString *attrStr = [[[NSAttributedString alloc] initWithHTML:data
documentAttributes:nil] autorelease];
NSString *plainStr = [attrStr string];
I'm not sure if there is a similarly straightforward way on the iPhone.