In the US there are no waivers for 250 KIAS below 10,000', except for the statutory allowance for climb performance (91.117(d)), and specific waivers for air shows and other special operations (91.117(a)). ATC cannot approve or direct any speed above 250 KIAS in cruise or arrival.
There may be different rules in other countries...
Last edited by Intruder; 6th Jul 2013 at 18:38.