VoIP apps allow mobile device users to place phone calls, send messages and complete other tasks using VoIP (Voice over Internet Protocol) technology. VoIP apps usually offer at least a few services for free and integrate with your device for seamless usage. The following are some of the top VoIP apps for both Android and Apple smartphones.

Android: Viber
With nearly 7 million downloads on Google Play, Viber represents one of the top VoIP app options for Android. The service issues push notifications to keep you informed about incoming messages and delivers audio with HD quality. Viber allows you to not only send and receive calls, but also to text your friends, relatives and colleagues at any time. Additionally, you can create messages with groups of up to 100 people and follow public chats.

The only downside lies in the need for all participants to have Viber. You can't call or text someone who isn't a member. Additionally, you might experience difficulty keeping a connection if you're in an area with no Wi-Fi service or poor 3G quality.

Apple: WeTalk
If you don't own an iPhone, your iPod Touch or iPad can work as a phone if you download the WeTalk iPhone VoIP app. It costs nothing to download the app or to make domestic calls. All you need is an iTunes account. It facilitates voice chat as well as push notifications. However, both users must install WeTalk to use it, and the service doesn't support emergency calls.

Android: Skype
If you want to video chat with your friends, Skype offers one of the best VoIP app options for Android. The crystal-clear video combined with enhanced sound and a clean user interface makes it an excellent choice. It also features fast, efficient text messaging and the ability to call landlines if you upgrade to the premium service. Unlike previous iterations of the app, however, it no longer allows you to send files along with your messages.

Apple: iCall
Geared toward small business users, the iCall VoIP app for iPhone allows you to place as many calls as you want to fellow iCall users for free. If you upgrade to the premium version for $2 per month, you can call landlines and mobile numbers as well. It also supports Bitcoin payments for users who prefer to avoid other payment methods.

Android: Lync 2013
This Android VoIP app for small businesses enables streamlined conference calls and video business meetings via your phone. Lync 2013 works on both smartphones and tablets. It proves particularly useful for telecommuting professionals and for colleagues who work in separate offices because the video conferencing feature enables fast access to your contacts list.

Apple: Talkatone
With Talkatone for Apple, you can use a nearby Wi-Fi connection to place and receive phone calls or rely on your device's data connection. Users who live in rural areas with lousy cell service will appreciate the ability to connect in multiple ways without installing a landline. It works on iPods, iPads as well as iPhones. The audio quality depends on the connection's quality, so users' mileage will vary. Calls to other Talkatone members cost nothing, but users can buy 60 credits for $0.99 if they want to place calls to non-Talkatone users.

Android: Nimbuzz Messenger
Social media users will appreciate the ability to connect Nimbuzz Messenger's VoIP app to their social media accounts, such as Google Plus and Facebook. You can call or video chat with other Nimbuzz members for free, or buy credits to contact other numbers through the app. Its user interface appears more dated than some of the other apps on the market, but it's user-friendly and easy to navigate.

Apple: Whistle Phone
If you prefer to use your iPad over your iPhone, the Whistle Phone app might solve your problem. Whistle Phone turns your Apple tablet into a phone with an app that allows you to place and receive calls without a mobile connection. Unlike many of these apps, Whistle Phone allows you to call landlines and mobile phones that don't use the same service.

VoIP apps work similarly to a traditional VoIP phone service. If you want to make phone calls from your mobile device without consuming your own minutes, using a VoIP app makes sense both financially and in terms of convenience. You should consider the ways in which you use your phone before selecting the best app for your device.

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