I honestly don't see the point of roaming at all. One can buy a prepaid SIM card in virtually any country now, albeit with some photo ID. There's not much that has to be said that can't be written in an e-mail, plus for sensitive information PGP is far more secure than talking on the phone. If you're paranoid.
When I'm overseas for business, I simply set my voicemail to reflect that and to inform people of my email address.
In addition, because it's not permissible for cellular phones to be locked to any one network in South Africa, the majority of people's phones will be able to accept any foreign SIM, no problemo.
However, as a lover of good humour, I find MTN's advertisement absolutely belly-rumblingly adverbially hilarious.