Apple ( AAPL) sank 4% in early trading after AT&T's ( T) early iPhone sales update underwhelmed investors.

Investors have been enthusiastic about Apple's prospects in the wake of the iPhone's introduction last month, and many on Wall Street were eagerly anticipating AT&T's update on activations of the new device. Apple introduced the iPhone the evening of June 29, so it was understood that AT&T's figures -- which cover the second quarter ended June 30 -- would reflect just a day and a half worth of sales.

Even so, the San Antonio telco's announcement Tuesday morning that it had activated a total of 146,000 iPhones on June 29 and 30 was met with something less than enthusiasm. Apple fans and industry analysts had been looking for about double that number.

Some iPhone customers did experience troubles activating their phones during the first few days of the debut. That may account for the some of the lower-than-expected tally from AT&T.

The iPhone did not fully sell out during the first week of the introduction, causing some disappointment among the most optimistic observers. As reported earlier this month, Apple's best-case-scenario goal or whisper number was to sell out the 1 million iPhones that the company was prepared to supply, said sources familiar with the plan.

Apple will report the actual number of iPhones it sold when it presents its earnings after the market closes Wednesday. The company is expected to report two categories related to the iPhone: the number of units sold, and a portion of the revenue, which is going to be booked over a two year contract period.

It's not likely that AT&T's iPhone number will be the same as Apple's. Merrill Lynch analysts expect Apple to report that it sold "at least a couple hundred thousand units at launch."

Early Tuesday, Apple fell $5.25 to $138.45 and AT&T slipped 32 cents to $39.76.

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