It has been a long time coming, but now the ASA has published some guidelines for advertising broadband.

thinkbroadband :: ASA publishes speed claim guidelines for broadband adverts
The Advertising Standards Authority (ASA) and Committee of Advertising Practice has published its guidelines on what broadband providers can claim in their adverts, no longer will people see figures like up to 16/20/24 Mbps in advertising, but rather smaller figures based on actual testing of the service. Providers have until April 2012 to bring their advertising into line with the new guidelines, mobile broadband data services are not required to toe the line totally, but endeavour to follow the spirit of the guidelines. Any marketing material must now only make a headline speed claim that at least 10% of customers can achieve, the effect on the figures in advertising are shown below.
For the full article, please visit the thinkbroadband site.

I see that the ASA still wants to rewrite the OED though. I've quoted from another source, but suffice to say I suspect that the OED may state something very similar.

thinkbroadband :: ASA publishes speed claim guidelines for broadband adverts
"Unlimited" are likely to be acceptable provided that:
  • The legitimate user incurs no additional charge or suspension of service as a consequence of exceeding any usage threshold associated with an FUP, traffic management policy or the like, and
  • Provider-imposed limitations that affect the speed or usage of the service are moderate only and are clearly explained in the marketing communication.

The element of the service to which the "unlimited" claim relates is a key consideration in this assessment.

  • A general claim, "Unlimited Broadband", for instance, will require a provider to demonstrate that their whole broadband service meets the criteria above.
  • A claim relating to a specific element (i.e. a defined activity or protocol) of a service, for instance, "unlimited web browsing", would only require the provider to show that element of service meets the criteria listed above. Broadband consumers are likely to assume that a claim related to "unlimited web browsing" will allow them unlimited use of the services such as You Tube, BBC iPlayer or another based streaming service. If an online activity like streaming is excluded from the "unlimited" aspect of the service this should be stated prominently.

Extracts from ASA report
Oxford Dictionaries:
unlimited
Pronunciation:/ʌnˈlɪmɪtɪd/
adjective

1 not limited or restricted in terms of number, quantity, or extentffshore reserves of gas and oil are not unlimited

Mathematics(of a problem) having an infinite number of solutions.
The possibilities with story problem math problems are unlimited.

2 (of a company) not limited.
This is because these retailers, along with a number of other top businesses, are unlimited companies.