It depends what axles you have and what the stock gear ratio is.
The 8.25 rear carrier allows 3.07 to 4.56.
The 44 rear carrier has two flavors 3.73 and down, 3.92 and up.
The 35 rear carrier has two flavors, 3.07 down, or 3.55 and up.
The front 30 has two flavors, 3.07 to 3.55, or 3.73 and up.
So, if your jeep has the 4.0L and 3.07 or 3.55 stock gears, you will need a front carrier to go with a lower (higher numerically) ratio. The rear totally depends on what axle is in there now, or what you will be swapping in, if a swap is planned.
To regear without adding the ARB or whatever, you would be paying 2x whatever the per axle labor cost is. Once to set the new gears up now, then once again when you got the locker installed. You will likely need another set of shims as well.
If you decided to get 'lunchbox lockers' vs the full case ARBs or whatnot, you don't have to set up the gears again... the lunchbox lockers install inside the factory carrier.