There’s a small but measurable iPhone 4S effect in November’s Millennial Media’s Media Mix, which reports the presence of various devices in the mobile advertising network it runs.

Apple (AAPL) was the No. 1 manufacturer in Millennial’s advertising platform, up 8% since October to gain a 26% share in the list of the top 15 manufacturers.

Meanwhile, in Millennial’s monthly pie chart of the mix of mobile operating system impressions, Google’s (GOOG) Android fell to 50% (from 56% in October) while Apple’s iOS rose to 30% (from 28%).

The effect — which can be seen in the two pie charts at right — is small but significant. Millennial is measuring advertising impressions on its clients networks, a secondary effect that reflects changes in the installed base rather than actual sales.

We’ll get a better measure of how much Apple’s share of the smartphone market has changed since the October release of the iPhone 4S when the company releases its unit sales figures for the quarter in mid January.

Millennial Media bills itself as the leading independent mobile ad and data network. You can download their monthly reports here.