Is it possible to run a 18w SOX with a 18w fluorescent ballast?   
If so, should I use a electronic ballast or a magnetic one?
Will this short the lifespan of my bulb?

I'm considering buying a SOX. Here in Brazil ain't no SOX, so I'll have to import.
If I can "cut down" the price of a SOX ballast, I would save a lot of money, because I wouldn't to pay the extra shipping price from the ballast.

Thanks for the answers!

Yes you can run an 18w SOX lamp on a normal 18w T8 magnetic ballast. 

I would guess the easiest is really the 18W "fluorescent" choke, just because the connection there is clear (plain series).
Technically it would be beneficial for the lamp to operate from a HF ballast, but to use a unit designed for fluorescents with a lamp not having the heater connection is not trivial at all.
You would have to determine the exact internal circuit (current vs voltage mode heating, lamp presence detection) and figure out the connection that will work with the SOX (to have the starting resonant circuit complete, to not short circuit the heater winding if the ballast uses voltage heating, to not let the current flow through components designed only for short exposure of a heater current, to maintain at least some ballast protection against missing/failed lamp,...).
Because the electronic ballasts differ in the internal circuitry, wiring diagram designed for one ballast model will very likely not work correctly on another.
And don't forget many makers keep the same model numbers and appearance while keep changing the inner circuit over time, so wiring correct for one piece may not suit the other made a year later...

Thanks.
You know a place where I can buy my SOX with a good price online? 

Yes you can run an 18w SOX lamp on a normal 18w T8 magnetic ballast. 

Just run up my 18W SOX on one of these and it (the ballast, that is) is running what seems to me to be a bit on the warm side, around 70°C (158°F) - is this ok..?

A thing about the HF ballasts

The expensive brand name ones vary

The cheap Chinese ones - I have not seen yet any one which is not the CFL current mode thing with just capacitor (and in best case PTC) across the tube

I've been trying this trick too.

I used an old 20W T12 choke - this should pass 0.38A, but actually stabilises at 0.40A and runs hot. The lamp follows the negative characteristic typical of and ends up at 49V, rather than the rated 57V. Circuit watts 34W. So, not too happy.

Then I tried an 18W T8 HF electronic ballast, with 10R resistors to simulate the heaters. It started and ran perfectly, but the circuit watts were only 17W and the  gave 25% less light than on the T12 ballast. Run-up was slower too.

Then I tried two 8W chokes in parallel - each should pass 0.16-0.17A into a ~60V  - and indeed I get a circuit current of 0.35A and the correct lamp voltage, but still a circuit of 35W! And (the two chokes are not the same model) one of them gets very hot - a sense resistor in series showed that actually the cooler one was passing 0.16A and the hot one 0.19A.

Perhaps the right solution is a proper 18W SOX choke! Rare as rocking horse poo, though.

Incidentally you can start the lamp with just an S10 glow-starter, or electronic starter, in parallel - or if you have one, a superimposed pulse ignitor for 70W Metal Halide etc.

Perhaps the right solution is a proper 18W SOX choke! Rare as rocking horse poo, though.

Incidentally you can start the lamp with just an S10 glow-starter, or electronic starter, in parallel - or if you have one, a superimposed pulse ignitor for 70W Metal Halide etc.

The lamps I have do start ok on just the ballast, but our mains is 245-247V, there is a substation outside the kitchen window..! I would like to get the proper gear, though, I'm a bit of a perfectionist with these things.