Mobile ad network Millennial Media is now putting out two reports on a regular basis: one about mobile advertising (SMART) on its network and the other about devices (Mobile Mix) on its network. Consistent with other networks and data vendors in the market, Millennial has seen considerable Android growth. But the iPad is also growing dramatically.

According to Millennial:

• Android requests grew 15% month-over-month, and have now grown 338% since January.
• The Apple OS remained the leading operating system on the Millennial network, but it had a month-over-month decrease of nearly 14%
• iPad requests grew 160% month-over-month
• For individual manufacturers, HTC received the largest share increase month-over month for the second consecutive month

Below are some of the report's charts, showing the hierarchy of devices and operating systems on Millennial's network. In addition, the company shows the percentage breakdown of developers working on the various smartphone operating systems.

Compare AdMob's most recent mobile metrics report (April, 2010) in terms of devices and operating systems on its network:

Other than the iPhone and the top three Android phones, there's a different array of devices on both lists. The top Android device on Millennial's list, the Nexus One, doesn't event show up on the AdMob list. The AdMob list shows no RIM devices among the top group, whereas the BlackBerry Curve is the number two phone over at Millennial. 

Comparing operating system share on the network also reflects the differences between Millennial and AdMob. Below is AdMob's US operating system share graph for April:

Millennial (top four):

• iPhone: 48%
• RIM: 19%
• Android: 15%
• Other: 8%

AdMob (top four):

• Android: 46%
• iPhone: 38%
• RIM: 9%
• Palm: 3% 

Each of these company specific reports needs to be taken with some caveats and caution. The discrepancies and differences between the networks illustrate this. However, both companies show similar trends: the growth of Android handsets, which makes sense give how many there now are, and the rise of the iPad (AdMob discussed that last month).