If you really want it you CAN have a phone & 10/100 down one CAT5e cable.(assume you have terminated to plugs rather than RJ45 sockets?) :-

2 X CAT5e Coupler-Straight Wired

2 x RJ45 & BT Double Adaptor

1 x 0.5m BT to RJ45 Patch Lead

1 x BT to RJ45 Converter, Master

Although a lot cheaper & easier to simply run some external telco cable down to the second socket!!