Milk is mostly water.
Instant coffee will dissolve just fine in milk or even cream.
Of course, flavour-wise it's going to be more like a weak latte than coffee.
That's essentially what a latte is - coffee and milk.
cooking.stackexchange.com/users/41/Aaronut
The principle is the same as adding instant chocolate milk powder to milk.
The end result is also similar: what you end up with is not so much coffee as it is brown-beige, caffeinated milk (so, something like a latte).
cooking.stackexchange.com/users/4587/Kenny Rasschaert
My grandmother's generation (in South Wales) would always make instant coffee using only hot milk.
I would ask for it made with water, but she wouldn't dream of doing that for a guest, for fear of appearing mean.
As far as I'm concerned, there are no issues.
With a suitable mug, you can heat the milk in situ in the microwave.
cooking.stackexchange.com/users/4214/slim
I put milk in a saucepan for 4-5 minutes on medium heat.
When I come back, the milk usually has a "skin" on it.
Remove that with a spoon, and then pour the milk into the cup.
I add a healthy spoonful of instant granules and some sugar, and it's as good as any coffeehouse leche...and way cheaper.
cooking.stackexchange.com/users/8816/Joelle
Just in case your coffee doesn't dissolve in milk.
You always mix your coffee with little bit of water before pouring in milk
cooking.stackexchange.com/users/2951/Foodrules 
There are places in NE USA and Canada where you can go in and ask for "coffeemilk" - it is usually made with real coffee.
Go to India and a lot of places will serve you "char" which is tea boiled up with milk.
Whatever floats your boat ...
cooking.stackexchange.com/users/5660/James Barrie
having instant coffee, or camp (chicory) coffee made with hot milk is the only way to serve it!
Loads of regional variations on what it's called, I just know it as a coffee made with milk!
It won't split the milk, and if you have 1 spoon of coffee when made with water, add at least half a spoon again when making it with milk to give a rich, smooth flavour.
cooking.stackexchange.com/users/47334/Glen
I add the instant coffee BEFORE heating the milk in the microwave for 2 1/2 minutes.
The coffee disolves better in the milk that way.
Also, I used rice milk or not regular milk, so it can be compared to skim milk in terms of consistency.
For even more added flavor I will add either cocoa powder or chocolate syrup.
cooking.stackexchange.com/users/None/
I usually just take a bottle (I have an eco-friendly aluminum bottle) and fill it with milk.
Then I add some instant coffee, a tiny bit of sugar(helps the grinds dissolve), and some cinnamon or cocoa powder (to flavor).
After that I just shake the bottle until it is mixed up very well.
The ratio to how much of each ingredient depends on taste.
And heating is really optional depending on how well you shake it.
During the summer I usually don't heat my coffee because... well it's hot during the summer.
Anyway, if you try it and like it then the answer is most likely yes.
cooking.stackexchange.com/users/6926/eMDeeBea
I also add the instant coffee before heating the milk.
It does make the instant coffee dissolve better.
Oddly enough, I also heat the milk for 2:30-2:45 like Melissa.
To top it off, I then add a creamer like International Delight into the brew and then mix it all together.
It is absolutely divine.
I personally don't like the taste of coffee that has been brewed in water.
It is too bitter for me.
Making it with milk seems to take away the bitterness and only leave the coffee flavor and whatever creamer I have added.
cooking.stackexchange.com/users/7191/Matt
The only thing you might want to consider if you are thinking of adding it to hot milk is a chance of splitting the milk.
I would suggest you mix it with a tablespoon of hot water before adding the milk.
Less change of splitting.
cooking.stackexchange.com/users/4283/notthetup
It's all about your palate and the flavors that you enjoy, like wine.
Try making it side by side with water, then milk.
cooking.stackexchange.com/users/5335/M. Torres
I grew up in Ireland & we drank this as kids.
It was made with Sanka .
This was easy to make, just pour milk into a sauce pan and then watch it to make sure it did not boil over.
Then we would throw instant coffee and sugar into the pot, stir it up, pour it into mugs and drink it.
Then we would make another batch 'lol' because even to a child's pallet it's 'friggen' great
cooking.stackexchange.com/users/35057/Adrian H Smyth
I like milk. So I thought of doing milk with instant coffee. I mean, I have coffee here but it says I should use water. I always use it with water and put a little bit milk.  Can I also use  only  milk without any water?
Instant coffee with only milk?
cooking.stackexchange.com
<coffee><milk>
cooking.stackexchange.com/questions/11637
cooking.stackexchange.com/users/6538/Johannes Schaub - litb
This is common in some countries, but you may want to mix the coffee with a little water first to avoid splitting the milk. Instant coffee will dissolve in milk. The flavour will be weaker than normal coffee.
Instant coffee will dissolve in hot milk. Many people do this. The flavour will be weaker than normal coffee and be aware of not splitting the milk.