PORTLAND, OR, United States – Think about this question for a second: what’s the primary reason you pick up your mobile device? Yes we like to make calls, run apps and even snap photos; but most likely the reason you reach for your mobile phone is messaging. Most of us rely upon SMS to reach our friends, family and everyone in between.

However, SMS, especially if you don’t have a messaging plan or perhaps if you message internationally, can get really expensive, really fast. We use instant messaging on our computers – and increasingly, we’re doing it on our phones as well. Here in the United States, your friends are likely spread across all the various IM systems including Google Talk, AIM, MSN Messenger, Yahoo Messenger and all the other systems that exist.

Also, some mobile-only IM systems are out there that offer benefits as well – let’s dive in and explore the various options:

Skype: Skype is dominant in the Internet calling realm. However, with hundreds of millions of downloads, Skype is also popular for instant messaging as well. Skype allows you to send messages to anyone you regularly talk to while on Skype on your computer. With Skype on your Nokia, you can share photos, videos, and other files from your phone. Also, if a Skype message isn’t available, you can send SMS for the cheap Skype global rates.

Nimbuzz: Nimbuzz (pictured above, right) is a hybrid client, in that they support other Nimbuzz friends and your traditional IM systems as well. Nimbuzz will allow you to interact with your friends on various IM networks including MSN, Yahoo!, GoogleTalk, Facebook, IM, MySpace and Hyves. Also, you can do free calls with other Nimbuzz friends in HD where supported. This app makes chats look good with customizable avatars and backgrounds for your chats.

IM for Nokia: This application, straight from Nokia, allows for access to top IM systems including Google Talk, Windows Live Messenger, Yahoo!, MySpace and Ovi Chat. You can customize your status and availability across multiple IM systems with one setting. One distinctive feature I like about IM for Nokia is that this application integrates your friends and contacts’ IM status straight into your contact list, showing you friends who are available right now.

eBuddy: eBuddy is most likely the one mobile IM app you’ve heard of. This long-time favorite supports all the popular IM networks and this application works on many different Nokia models. A year ago, CEO Jan-Joost Rueb reported to Conversations that they support over 900 Nokia models. Also, back in April it was reported that eBuddy hit 10 million downloads int he Ovi Store – which is an astonishing figures.

WhatsApp: I wrote about WhatsApp earlier in May, but this app is distinctive enough to warrant another mention. WhatsApp allows you to communication with contacts, either on a 1:1 basis or as a group. If your friends have other phones, such as iPhones, BlackBerry or Android, WhatsApp facilitates instant communication with them. Also, WhatsApp can degrade to SMS if this is necessary. WhatsApp can send pictures, audio and video to multiple parties, making this app very useful.

Which of these apps to you use? If none, what mobile IM app do you prefer? I look forward to a lively discussion below, based on your experiences