I actually switched to Ooma from Vonage about a month ago and signed up for Ooma Premier 1 year which came with a freebie that I used to get a free number port from my old number. After filling out the form on a Thursday night it was completed six days later on Wednesday. They had orginally said it would be about 2 to 3 weeks.
I double and triple checked the info I provided in the number porting application because I heard any mistake could mean a long delay. I also uploaded a PDF copy of my latest Vonage bill.
So if you decide on Ooma it could take just a week or less!