I have come to United States an year ago to pursue my masters. In the beginning days, I had no mobile, no laptop and no similar gadget with me. It was hard to communicate and roam around without these things. But I have learned many things which can help you when you travel to United States. There are many mobile apps and online services which can help you in your transition and later too. Here we go:

It is better to get a either a smartphone (I prefer Android and make sure it works in USA), a laptop or tablet when you come to USA. Otherwise buy one after you arrive. Most of these apps or services are recommended assuming that you have an easy access to internet and Wi-Fi connection.

Communication

1. Google Voice [PC/ Linux, Mac, Android]

   If you have a personal laptop or a PC, you can use Google Voice to make phone calls and SMS across the United States for free. There is also an Android app, but it works only if you have a mobile service. I mean to say that the Google Voice Android app does not work if you do not have a SIM card, but you can make calls from your computer/ laptop from Gmail. You can add a few bucks to your Google Voice account and use it for cheap international calling.

2. UppTalk [Android]

   There are many free calling apps for Android in the United States. I have tried many of them, but felt this was better than the flock. If you have a mobile device and do not have a SIM card or mobile service yet, this can come to your rescue. You will be assigned a number and you can call anyone in the US and receive calls for free. You just need WiFi connectivity for this to work.
   

3. call2friends.com [Web with flash plugin]

   This website provides limited free calling to many countries. It provides free calling to India for a minute per day and for United States for about 3 minutes (at the time of writing this post). Although this does not sound a good alternative, it helps sometimes. I was using this to call my parents in India and ask them to come online on Skype. I used to use Google voice from my laptop for calling from the United States and used this website to notify my family or friends to appear online. 

4. Facebook Messenger [Android, iOS, web]

   Not yet popular, but Facebook messenger has recently added a feature to make voice calls. This is an awesome feature and can help you, call your friends anywhere in the world and that too without having a mobile number. However, to make a call the person on the other side should also have this app installed. The good thing is that most of the people in US have a smart phone, WiFi connection and this app installed. We may not have phone numbers of all our friends, but we have most of our friends on Facebook which makes this app very useful at times.

5. Calling Cards

   There are many proxy calling services using which you can make cheap international calls. I hardly use these services as I go with Google Voice but most of my friends do. Most of my friends use indiald.com, telcan.com and other similar services to make cheap calls to India. You can give them a try if needed.

Finding Accomodation

There are many services which can help you find vacant houses around you. Here are the ones which I felt can help you out.

1. Zillow.com

   This is an excellent app to find houses around you. It has both a web version and an Android app. The Android app can find houses round you based on your location. It marks vacant houses on a map and we can also search by distance from your location. But this app may not show all the vacant houses around. Its database was not that good at the time I used it.

2. Trulia.com

   This is similar to Zillow. I hardly used this app, but many people and tech blogs recommend this. Also, it has better ratings on Google Play and seems to be more popular than Zillow. There can be many other houses not listed on these apps, so it is always a good idea to check by visiting local real estate agents.

Split Expenses

1. Splitwise.com

   Most students and employees plan to live in a shared apartment after arriving in the US, at-least in the first few months unless you are rich enough. If you are sharing an apartment with your friends, you may have to split expenses among your roommates. This app does exactly that and simplifies a few complex calculations and saves a lot of time.

2. SplitEasy

   SplitWise is a good service, but we had a bad experience with it. A few entries got modified or, deleted without our intervention. Mistakes in financial matters is not always a tolerable issue, so we planned to make a software of our own. I started coding it on a fine weekend in Python and we have replaced SplitWise with this for our in-house purposes. This uses entries from an excel sheet and does the calculations. I don't recommend you use it in the present state (at the time of writing this post) as it is not well documented and doesn't have a pretty interface. I will post it on my blog at all if I document it and make it user friendly.

Other

1. Explore around you with Google Maps

   You can use the Google Maps Android app to easily find places around you like restaurants, gas stations, parks, offices, etc. In the current interface, if you click on the user icon on the right-top corner, you will be shown places around you in categories. You can also find user ratings to all the places. That's a very helpful feature if you are new to that place. I recently went to Seattle on a vacation to my sister's house and this app helped me a lot. Every day in the evening, I used to open this app and plan for my next days' trip. I've enjoyed a lot in this vacation and thanks to Google Maps.

2. Did I miss Anything?

   I have listed apps and services that I have used and felt are also be helpful to you. But that does not mean I am aware of all the wonderful apps and services. Let me and other readers know if you know any other good apps or services. That would be very helpful.

Most of these apps may work for you everywhere independent of the location, but a few of them are relevant only for the United States. Some of my friends are coming to the USA to pursue their higher education and a few are coming on some job and some of you can be tourists. Whosoever you are, I hope this post helps.