To stay in communication, you can either:
Use your phone to connect to wifi and use WhatsApp. While this should be free, there may be places in the Netherlands where you cannot find public wifi.
Purchase an international plan through your wireless carrier. This should allow you to use either 4g or wifi.
Buy a data SIM card upon arriving in Europe. I suggest checking with your carrier here in the US before leaving, but most iPhones and Androids are "unlocked", meaning they can accept a foreign SIM card. Plans/deals/roaming charges etc. are always changing so ask questions to be sure you're not getting ripped off. Vodafone is a good option with service in the Netherlands: https://www.vodafone.nl.
Public transportation in the Netherlands is extremely convenient and quite expensive. Before complaining about the expenses, think about what it would cost to accomplish the same transportation needs in the US, where you would need to rent a car, buy gas, get insurance, find parking, etc. Budget accordingly and marvel at the convenience of the system.
Chipcard
You can buy an anonymous OV-Chipcard. This works on all of the public transportation systems. You can buy one at the airport or at Amsterdam Station. You will probably need to visit a counter to purchase your card but it can be reloaded at an OV machine. I suggest putting at least 50 to 100 Euro on it. Make sure to chip in and chip out every time you use transportation or your balance will be drained.
Railpass
You should investigate and a decide if a rail pass is a good option for you. You need to be careful because the passes have restrictions that might not make them applicable to our various day trips outside of the cities.
Bike Rental
You can also use bikes to get around just about anywhere. Some private companies provide bike rentals by the day or week.