You'll certainly lose service for a little while when being ported, but they tend to do it in the small hours of the morning so it's not a big deal.
Except of course occasionally they stuff up. Then you might be cut off for a day or two while they sort it out.
But, heh, life is still possible without a mobile phone!
On business cards you're being ripped off. I just checked with out office manager and confirmed that we pay $134 for 200 pcs, double-sided 2-colour. They do the artwork. If we provided the artwork it would be $70 for 200pcs. Delivery is 2-3 days.