Upselling on the phone or in person is a completely differnt thing than in e-mail, newsletters, etc. If someone can simply ignore, delete or throw out the upsell there is no perceived pressure. If you are on the phone or in person they feel held hostage while you berate them with offers they didn't call for and most people don't want or can't use.

Which is why McDonald's wants you to upsell EVERY time. If you offer one hundred people the option of an additional item or a value meal, etc chances are higher someone will take you up on it.

Another option could be an upsell on the "order form" based on the hosting options chosen.