I refer here to Sean Owen's Barcode Contents. I made sometimes minor changes in the quotes (URL change and adding more examples for sending SMS), but remained true to the text.

URL (Mobile Web address) - Example

The most common application of barcodes is to encode the text of URL. To do so, simply encode exactly the text of the URL in the barcode: "http://anyurl.mobi". Include the protocol ("http://", here) to ensure it is recognized as an URL.

Readers should open the URL in the device's web browser when decoding a URL. It is probably desirable for a reader to display the URL and ask the user whether to proceed, so that the user may see the URL before accessing it.

Agree 100% and we think it's important that the user chooses to proceed or not. - Kaywa Reader works like this. If possible do not use capital letters for URL's.

E-mail address - Example

To encode an e-mail address like sean@example.com, one could simply encode "sean@example.com". However to ensure it is recognized as an e-mail address, it is advisable to create a proper mailto URI from the address: "mailto:sean@example.com".

Agree 100% - Kaywa Reader works like this

Telephone numbers - Example

A tel URI should be used to encode a telephone number, to ensure that the digits are understood as a telephone number. Further, it is advisable to include prefixes that make the number accessible internationally. For example, to encode the US phone number 212-555-1212, one should encode "tel:+12125551212". This tel URI includes a "+1" prefix that will make it usable outside the United States.
Readers should invoke the device's dialer, if applicable, and pre-fill it with the given number, but not automatically initiate a call.

Agree 100%, also about not initiating a call automatically. Kaywa Reader works like this.

SMS - Example

Much like an e-mail address, one can encode an SMS shortcode or number by creating an sms URI. For example to create a link to the number "12345" one would encode "sms:12345" or "sms:+12024561111?body=hello%20there" or "sms:+12024561111,+15102061079". See this draft of the SMS URI specification for details.
Readers should open a new SMS message, ready for the user to compose and send it.

Difference! The Kaywa Reader used and uses currently smsto! I think if we have mailto, smsto would make more sense. If there is a standard (right now it's a Draft) however, everybody should try to follow it.

Contact information - Example
The trickiest of all and the least standardized.
There is vCard, MECARD from NTTDoCoMo and another KDDI format.
Kaywa Reader uses vCard Standard for Name, Email and Telephone Number.

BEGIN:VCARD
N: Your name
EMAIL: Your email
TEL: Your phone number internationally
END:VCARD

For international use, I think vCard is definitely the way to go. It's a bit more verbous than MECARD, it's true, but people do not have to learn another format. The optimum would be to support both MECARD (established in Japan) and vCard (established here).