@JaK is correct in his answer. If you are more curious as to why you are getting this message and how everything works check out this post: http://productioncommunity.publicmobile.ca/t5/Discussions/If-I-text-or-call-a-local-number-while-the...
Whether or not a call is considered "long distance" has in fact nothing to do with your plan but rather is still based on the original phone system model. Your plan determines whether you will be charged for the "long distance" call. In order to access your voicemail your phone has a stored access number (usually this is actually your own phone number - when you call your own phone number from your phone it will access your voicemail). If you have a Toronto number and are in London, when you access your voicemail you are actually calling your own phone number (a Toronto number) while you are in London. This is considered a long distance call and hence you receive that message indicating that long distance charges may apply. If you have a province wide plan, these long distance charges wont apply to you though the call is considered "long distance" --> your province wide plan includes long distance calls within your province, hence you will only be charged for long distance calls that are not covered by your plan.
If you dont want to be bothered with hearing this message "long distance charges may apply" when you make calls --> add 1 in front of the number. In this case you would have to change your voicemail access number in your phones storage by adding the suffix +1
Back in the day, instead of a message saying "long distance charges may apply" the recording would actually tell you to hang up and place the call again with a 1 in front of the area code. Nowadays they just patch the call through for you, but warn you long distance charges *may* apply. If you precede the number with a 1 they assume you already know long distance charges may apply and do not give you any message.
