The Mobile World Congress in Barcelona is long over for this year and it hasn't really been my focus, but I also had a look at how well the exhibition ground for the Mobile World Congress was covered for non-3G users.
While many if not the majority of the MWC attendees had 3G phones I am sure there was still a sizable percentage of people with 2G Blackberries and other GSM only phones. Even with my 3G phone I was mostly using the GSM/EDGE network due to Vodafone Spain's battery killing network configuration when being always-on. While I haven't checked how many cells Vodafone had deployed and if they had dedicated coverage in the exhibition halls, I can nevertheless report that unlike during other exhibitions I have been in the past, incoming and outgoing calls worked fine throughout the week and I saw no degradation in download speeds for my e-mails and while browsing via Opera Mini.
Especially when web browsing, one can immediately feel the difference between a loaded network in which only few timeslots are available for data transfers which on top are heavily used for example by Blackberries. But no, everything was fast and swift, despite probably more than 20.000 people being at the exhibition simultaneously.
So kudos to Vodafone Spain, your 2G network was working fine as well.