As a person who makes money developing Android apps, I have to tell you that you probably want . . . a mobile website.

A mobile website is probably 5x cheaper. Imagine hiring a developer for every platform instead of expanding the web development team you probably have.

HTML5 is said to be the way of the future.

Amazon has an Android App AND a mobile website. They don't look very different in style. I like the mobile site somewhat better.

For $50-100 bucks, you can find several websites that will create an app that just launches your mobile website. Then you can say you have an app.

There are a few exceptions:
If the store is for things people will use on the phone: ringtones, mp3s.
If you can make it a compelling vertically integrated tool.

Example: Shop at Ted's Model Rocket Supplies isn't all that compelling as an app.
But a Model Rocket Designer App that lets you design and simulate your own model rocket using a 3D interface and then push a button to order all the supplies you need in one click - that's more compelling.

- Is there some made solution to integrate existing shopping cart values into mobile cart purchase?

- Do you prefer Apple Apps or Android as you posted you currently develope such Apps.

- What language should be used to develope mobile websites from existing ecommerce website in modern way?

There are many languages ways:
PHP, JavaScript, AJAX, XHTML Mobile Profile (XHTML MP), Wireless CSS, WAP 2.0, Tera WURFL, MyMobileWeb, Mobile Web Toolkit, Image Server, GAIA Image Transcoder, HAWHAW , ready.mobi, Nokia's Mobile Internet Toolkit , SMIL, Voxeo's Prophecy server, VoiceXML (VXML), grXML, Frost library, WALL, WURFL, SMS, MMS, mobile payment gateways, mobile widgets, Mobile AJAX, Android, Google Gears, and Dojo Offline

Amazon has mobile website which is not clear published.

I have found some URL:http://www.amazon.com/gp/aw/h.html

- Is there some made solution to integrate existing shopping cart values into mobile cart purchase?

A web search says yes. mobi-cart is one of the top ones that comes up - there are others. I can't reccommend anything

- Do you prefer Apple Apps or Android as you posted you currently develope such Apps.

What I prefer is irrelevant. Android just surpassed iPhone in market share in the US, but Apple users tend to be more willing to spend money.

If you covered those two, you;'d have a good chunk of users.

- What language should be used to develope mobile websites from existing ecommerce website in modern way?

CSS.

There are many languages ways:

I don't have the experience to tell you exactly what to use. Find a shopping cart software that meets your needs, and add mobile capability to the musts list.

For example, I will probably be posting to the ecommerce forum because I'm looking for a shopping cart solution myself.
I want it to have:
Digital downloads of large files (100MB - 1 GB).
Possibly order the same digital downloads on DVD.
Sort offerings by state, region, activity, and tags.
Be SEO friendly.
But in addition:
Should have capability to display a mobile version (when the user agent requires it) and look awesome.
Should be compatible with some of these mobile shopping cart apps or app generators.

Amazon has mobile website which is not clear published.

Here's the secret: if you go to amazon on a mobile device, it will look way different. Its loading a different theme or whatever based on the user agent.
This is what your site should do too.

Thank you. Seems you are very good in mobile applications.

Nice feedback.

If you have nothing new to bring with an app, just stick with a mobile site.