The iPhone and iPad automatically adds hyperlinks to things it thinks it knows how to handle, like linking dates to the Calendar app and phone numbers to the dialer. (Several desktop email and webmail systems do this too, especially for dates.)
You can prevent this by breaking up the values with an invisible character that throws off the text detection algorithm, like the Unicode "Zero Width Space" character (​). This character is totally invisible in every email client, but it succeeds in "breaking" the iPhone date/number/address detection.
An Example (iPhone adds blue links to the number and address):
<p>Your order confirmation number is 5568321321 and a sample address is 123 Main St, Washington, DC</p>
The iPhone will add blue links to the confirmation number (mistaking it for a phone number) and the address.
Now add in a couple Zero Width Space characters:
<p>Your order confirmation number is 55683​21321 and a sample address is 123​ Main St, Washington,​ DC</p>
And it looks exactly the same as the original, but with no auto-linking of values.
Bonus: This also works for disabling auto-linking in GMail.