Unlock Message: "From Buckingham Palace to Brick Lane, The Savory Hotel to Soho Square, and Downing Street to Diagon Alley, you’ve seen the city’s best... and all before teatime. Add a spoonful of sugar for us! Well done, chap."

Just got.
First follow their page on the new cities page.

Then the it first 5 check-ins:
Hyde Park
Portobello Road
Canary Wharf
Soho Square
Primrose Hill

https://foursquare.com/4sqcities/list/london-calling

Then do the same for Istanbul and Paris !!

https://foursquare.com/4sqcities/list/la-villelumière
https://foursquare.com/4sqcities/list/bosphorus

@MartininBrussels wow..haha great search and effort, your paris link not valid

Previous check-ins count... just unlocked with one check-in.

The link is valid. You need to copy and paste, the è messages with the fourm code.

Yeah, sorry Jimmy

https://foursquare.com/4sqcities/list/la-villelumière

That should be better. But the great news is that this is just the first 3 cities... There will undoubtedly be tons more...

another MOG glitch :-D

got my badge with 3 checkins

kuala lumpur batch please!! :P

4sqcities was categorized in 4sq core badge....

I got this one with 1 checkin at Picadilly Circus. Past checkins must count as most the places on the list were also for the History London badge.
On a different note I did not have to follow the list but must follow Foursquare Cities.

Got my Badge in 2 check-ins...But i guess i could done it by one check-in in Piccadilly Circus as what @Bren told us, and yeah previous check-ins count also.

for some reason i unlocked with just one check-in.

Here are the 5 links I used.

http://m.foursquare.com/venue/4ac518d2f964a52026a720e3
http://m.foursquare.com/venue/4c1cdc88b306c928077c64b7
http://m.foursquare.com/venue/4c513de4250dd13a41a4e17c
http://m.foursquare.com/venue/4ac518cff964a5206ba620e3
http://m.foursquare.com/venue/4b2e246ef964a520f9dc24e3