Basically if your just going to be checking emails throughout the day or looking on pf etc each day then it should be enough for a month yes, if however you will be looking on sites like youtube or other video sites which use alot more megs then you will use more than that i expect, so it really does depend on what you will be using the mobile internet for, but you can keep an eye on that figure by going to a option within the phone.

What phone is it? does it have wifi? if it has wifi that means it also has wireless internet, meaning you can connect free of charge as long as the wireless is public/open without a password you can join and surf for free, and obviously if you have wifi at home you can surf until your blue in the face, you wont be charged because your using wifi. Hope this helps, ive tried to explain in simple terms