At Continental/Express, the chimes are as follows. The doorbell is front F/A to back F/A, or from Cockpit. The single chime/ding (depending on aircraft) indicates either a sign change (seatbelt or smoking sign of or on) or a passanger call button. At 10,000 the captain will normally give two chimes/dings by releasing the no smoking sign then turning it back on again, thus the two dings. This will be associated with a blue steril cockpit light over the cockpit door. The light is on below 10,000 and off above 10,000 roughly. Below 10,000 the flight attendants should not call the cockpit unless there is an emergency. If they do call, the pilots might take a bit longer to answer the call as they are prone to be more busy below 10,000.
Returning through 10,000 feet on landing, the cockpit crew will turn on the steril (blue) light but not necessarily issue a chime with it. 10 minutes from touchdown the cockpit crew will give the flight attendants 2 dings (again the no smoking sign off, then on) and the flight attendants will start with their "could you please help in preparing the cabin for landing" announcements.
On a side not, it upsets me when the flight attendants get the two bells and then announce to the passangers that "we've been cleared to land". Amazingingly stupid. Ten minutes can easily be 40 miles from the airport and you are normally cleared to land about 5 miles from the end of the runway. I wish they would quit that crap as it makes the pilots look stupid if there is an unexpected hold/go around or something of that nature. "But I thought we were cleared to land a few minutes ago, why are we climbing?"
On the ERJ, passing 10,000 feet going up and down, we have a special button that gives a doorbell sound. It gives no light on the pa system so the F/A knows to look for the steril light and make an announcement. Some pilots use that button twice for the two bells 10 minutes from landing. Most use the no-smoking sign as I do. It makes 2 real bell sounds. 4 bells at COEX is prepare for inpact and 2 ding-dongs can confuse someone as being 4 bells. I like to keep is simple.
Actually flown: EMB-120 EMB-145 B717 B737 B757 B767