I suspect there are very few pilots who willingly fly into Class B airspace without a clearance. And anyone desiring to do so should at least have enough common sense to use a stealth aircraft. And, as far as I know, F-117's are a little difficult to rent nowadays (but a Cessna 172 might still sneak you into Moscow if you're game).
Figure 1 shows the eastern end of Class B airspace for Los Angeles International airport. Positions A & B show Victor airway 186 intersecting Class B airspace in a northwesterly-southeasterly direction. If you're flying V-186 in a northwesterly direction (position A), the shelf of Class B airspace in that vicinity begins at 9,000 feet and tops-out at 10,000 feet (position C). Further along the airway, the floor of Class B airspace lowers to 8,000 feet (position D).
Here's the problem. Suppose you're flying VFR, northwesterly on V-186 at 8,500 feet, while receiving flight following (basic radar service). If you stay on the airway, you'll eventually clip the corner of Class B airspace. Does the communication you've established with ATC for flight following constitutes the required ATC clearance to enter Class B airspace?
The answer is "NO."
Just because you're talking with ATC doesn't mean you have a clearance through Class B airspace. In the case of Los Angeles, this is especially relevant.
The controller providing radar flight following on V-186 is in a different city than the controller who owns (and is responsible for) this parcel of Class B airspace. Your controller must obtain permission (usually via telephone) from the Los Angeles controller before you can enter that small section of airspace. That's why you should never assume that a clearance into or through Class B airspace is implied just because you're in contact with a controller. Unless it's specifically stated that you're cleared through or into Class B airspace, you should ask the controller for a clearance.
