If the load is rated at a genuine 2A peak then you need to provide a means of supplying it. If you want to avoid a brute force approach then knowing the worst case power profile would be of great assistance.
Placing a maximum current limited on the input to your power supply is OK if it is useful to do so, as long as you can obtain the average power level required and can service the peak output load. Placing a current limiter between power supply and modem guarantees failure.
The easy and obvious way to provide brief current peaks which are well in excess of suspply capability is to provide output capacitors. 1 farad will drop by one volt in one second when supplying one amp.
Or, rearranging in various ways:
dV = I.t/C | C = i.t/dV || t = C.dV/i || i = C.dV/t
These formulae (all the same formula rearranged), can help you make decisions about output filtering.
If the 2A peak lasts for 1 uS you need C ~= i.t/dV = 2 uF for 1 Volr drop = not much.
If the 2A peak lasts for 1 S you need C ~= i.t/dV = 2F !!! - largely supercap country.
What they probably have in mind is peaks in the uS to perhaps 10's of mS range that can be supplied by large conventional capacitors. For say 10 ms duration & 1 V droop.
C = i.t/dV = 2. 0.01 / 1= 0.020 F = 20 mF = 20,000 uF.