Originally Posted by
kellytoronto
so is it still the case that you can upgrade a m/u Tango Plus with the 2009 SWUs?
Yes.
And until Feb 28th I believe that you can still do an instant update with an SWU. As jarosba says, the only way to be sure of getting an M or U fare is to call.
Not all routings have M/U fares available, so you might want to check KVS or ExpertFlyer for published fares on routings. Some, such as YYZ-LHR are very good deals, other not so much.