Michael Olson from PiperJaffray made some interesting comments in a research note released last week. In his analysis, he concludes that the aged installed base of iPhone will contribute meaningfully to iPhone 8 refresh. He also believes investors/analysts will transition towards valuing Apple shares on a sum-of-the-parts (SOTP) basis. Olson reiterates his $155 price target, and his overweight recommendation.Here were the key highlights from the report:Apple's higher margin services revenue segment grew 22% y/y in FY16, materially outpacing the other segments. At only 11% of total revenue, however, it is a stretch to expect investors to consider using a sum-of-the-parts valuation on AAPL at this point. As services revenue climbs closer to 20% of overall revenue in the coming years, we do expect a shift toward a SOTP methodologySpecifically, our analysis suggests that at the time of iPhone X launch there will be an installed base of ~315M users on an iPhone that's at least 2 years old (see details in table below). We believe a sizable portion of these users, in addition to users with newer devices, will look to upgrade due to the age of their device and the more significant changes to the device.Olson’s reasoning sounds well supported, and while his estimate on iPhone shipments at 240 million is higher than consensus estimates. I believe, iPhone 8 will surprise expectations set by analysts in the next fiscal year, given feature updates, pent-up hype, and likely adoption among the aged iPhone installed base.I reiterate my high conviction buy recommendation and $156 price target.