As Fox says its quite common.
Its basically to stop fraud, ie to ask for compensation for a loss/damage that had taken place before the policy was in force from claiming to have taken place once the policy was in force. 14 days is deemed enough time for most people to not manage without their mobile phone.
Another example I can quote is Car breakdown, there is a 24 hour period after taking out RAC/AA membership when your not covered. Exactly the same reason, they don't want people breaking down, taking out membership and calling 5 minutes later to say their car has broken down. I think there are sometimes exceptions to this rule but thats the basic rule. 24 hours is deemed enough time for car breakdown that most people would need to deal with the situation before then. But you could for example if you had more than one car (or could use alternate transport) and your car wouldn't start at home, take out the policy with home start and call 48 hours later. A tow truck from most garages costs about £90 so you could find taking out a years breakdown cover including home start would be less.
