With Verizon or SBC, this is a distinct possibility. Often they'll let you grab two dynamic IPs from the same phone # withough billing you any extra (I've used up to 6 before!). Just throw a little hardware router or make a Linux router out of an old PC... Bam! You're good to go
The sad part is I've got a K6 450MHz system ready to go...I'm waiting till the weather improves to do the modding on the case tho...that and the time I need to design and plan the mod.