I am currently on a valid H-1B with company A. The visa stamping in my passport expires Dec 1, 2006. Now, if I transfer my H-1 to company B, then can I travel abroad and re-enter the US before Dec 1st, 2006 on the visa of company A but an approval notice (I-797) of company B? Or is it advisable to get the visa stamping with company B info before traveling abroad?