[patio11]

It's because everyone in Japan started sending SMSes to everyone they knew practically before the shaking stopped and that DOSed the network. This happens fairly regularly (e.g. for a few minutes after midnight on New Years, when a large portion of Japanese people send well wishes within the same 15 second window).

[eru]

From my experiences in Germany, SMSes send around midnight New Year did sometimes take several hours to arrive.

[neves]

In Brazil the SMS network stop working during Carnival celebrations. You can't talk due to loud music and everybody is trying to meet their friends.

[Cafesolo]

Same in Argentina.

[uxp]

Although it may not have happened in this instance, cell towers are prone to fall down if shaken violently.

[ars]

I suppose it could happen but prone? Especially a guyed tower should not fall down even if shaken.