routing via single provider

Hello everybody. We are the new LIR, recently received our first allocation and assignment. For now we have connection with only one service provider, so we can't register our AS-NUM (but we will do in near future). How do we establish routing via this provider? And after that, if we establish routing via this single provider, and then connect to another provider, register our AS-NUM, how fast and easy will it change - from direct routing to BGP? Will it be noticed by users? Thank you in advance. -- Best regards Alexander Lunyov OJSC RTC