The yellow pages business will soon be history at Qwest ( Q). Luckily for investors, the company will have a stack of bills by which to remember it.It's not enough that the teetering Denver telco soon will part with one of its most profitable lines of business. In its haste to do the $7 billion, two-part deal, observers say the company left standing several agreements to subsidize local phone rates with the proceeds of a directory business that it no longer will own. Some investors say that the fact that Qwest left those subsidy agreements in place shows how desperate the cash-strapped, debt-encumbered company was to do a deal. And they say the cash drain that the subsidies represent is one that Qwest can ill afford as it faces the prospect of credit-line negotiations as well as billions of dollars in debt-repayment deadlines in the coming year. Despite those worries, Qwest shares rallied Tuesday, adding 71 cents, to $2.95.