Airbnb is busting at the seams in the United States, so the company is now opening six new international offices in the first quarter of this year. Barcelona, Copenhagen, Milan, Moscow, Paris & Sao Paolo will soon have an official Airbnb presence so the company can work on building communities for its service there.

Since its launch in 2008, the marketplace for room rentals has booked over five million nights in people’s homes and properties. Four million of those have come in the past twelve months. The service has become so popular that many people in major cities like San Francisco and New York have found it to be a fantastic extra source of revenue.

The most interesting trend amidst all of this growth is the fact that 70% of the listings on Airbnb are international. The international nuance of Airbnb has caused the company to expand its support team by 12x, and now does 24-hour customer service in 16 different languages via live-chat.

Here are some more stats that show the impressive, and surprisingly international, growth of Airbnb:

• Over 100,000 properties in 192 countries, and over 19,000 cities worldwide, are listed on Airbnb
• Over 75% of all reservations in 2011 were international, with either the guest, host, or both located outside the United States
• Guests have traveled over 1.2 billion miles (2 billion kilometers) through Airbnb – enough to travel round trip from the Earth to moon 2,500 times

With traction fueled by its iOS app and recent entry into the Android Market, Airbnb has become a popular, and at times cheaper, alternative to booking hotels. After a monster $112M round of funding last July, the company is poised to take more market share away from popular hotel chains. This type of disruptive shakeup is similar to what we’ve seen with taxi-replacement service Uber, which announced its intention to expand into 25 new markets last December.

Click the image below for a closer look.

According to a report by Macworld, Sprint has set the record straight on getting an unlocked iPhone 4S from the company.

Originally, Sprint and Verizon were said to NOT be able to have the carrier-agnostic phones, as it was most likely locked down in software. Later, it was reported that Verizon would unlock your device if you paid your bill on time, but Sprint would not.

Sprint will now unlock your iPhone 4S if you request them to. The only way to be assured of an unlocked iPhone purchased with a carrier contract from day one is through AT&T, and that option is available on November 1st. Unlocking an iPhone is essential to be able to use the device worldwide.

The Sprint iPhone 4S ships with a micro-SIM slot unlocked, but Sprint now says that it will lock the slot via an update shortly after shipping. After the slot has been locked, customers in good standing can request the unlock. There is no time limit on this, but you have to prove that you are in good standing.

Verizon, on the other hand, has said that the company will unlock your iPhone’s slot once you’ve had it for 60 days and your account is in good standing.

Here is a statement from Sprint on the matter:

Sprint’s policy is to have the iPhone 4S SIM locked to our network domestically and internationally. At launch, the International SIM will be unlocked. We do expect a SIM lock to be pushed to the devices shortly after launch. We will then allow existing customers in good standing to unlock the SIM for international use if needed in the future.

Customers can sign up for one of our international rate plans and use this phone all over the world. When traveling internationally, there is a setting that must be turned on within the device to connect to GSM. The phone will work with a SIM that is provided within the device out of the box. International voice and data charges are on a pay-as-you-go basis and vary based on the country where the customer is using their phone; a list of rates is available at www.sprint.com/international.

Sprint offers two international voice plans that customers can subscribe to for discounted voice rates:

The Canada Roaming add-on is $2.99 per month and all calls placed from Canada are only 20 cents per minute. Without this add-on, calls from Canada are 59 cents per minute.

The Sprint Worldwide Voice add-on is $4.99 per month and offers discounted rates in countries around the world. For example, calls from Italy are $1.69 per minute with this add-on or $1.99 per minute without the add-on; calls from Peru are $2.29 per minute with the add-on or $2.49 per minute without it.

It may sound confusing, but if you absolutely need an unlocked iPhone 4S as soon as possible, AT&T still looks to be your best option right now. All you have to do is swap the SIM card.