Following my request for people to test their own mobile provider, here is an up-to-date summary of responses so far. The number under "Modifies" or "Doesn't appear to" is the number of individual confirmations I've received. I won't update this after I've received 4 consistent responses.
|Country||Operator||Modifies||Doesn't appear to|
|Netherlands||T-Mobile||*||* (Note 1)|
- T-Mobile in the Netherlands apparently gives users a choice when they subscribe to the service.