Take it all the numbers with some caution (see below). MediaPost reports on IDC's estimates of the revenues of various mobile ad networks (some figures are global and some US only apparently).

IDC says that Google-AdMob's (GoogMob's) mobile ad revenues would be worth $68 million, or 24% of the overall market.

Here's the full list and their IDC-estimated revenues:

• GoogMob: $68 million
• Millennial Media: $51 million
• Yahoo: $32 million
• Microsoft: $23 million
• Quattro Wireless: $21 million
• JumpTap: $11 million
• AOL: $7 million
• Others (the largest single chunk): $73 million approx.

Update: I'm getting some feedback from a couple of reliable sources that these numbers may be close in a couple of cases but are otherwise inaccurate.

Here are some other numbers from an article that appeared in AdAge (by Rita Chang) on October 12, 2009. Estimates are based on inferences and interviews with a number of parties:

• AdMob
  Estimated 2009 sales: $40 million (global)
  Total funding: $47 million; last round in Jan.
  
• JumpTap
  Estimated 2009 sales: NA
  Total funding: $72 million; last round in Aug. 08
  
• Millennial Media
  Estimated 2009 sales: NA, though CEO Paul Palmieri said $10 million was a "great quarterly goal."
  Total funding: $21 million; last round in 2007
  
• Quattro Wireless
  Estimated 2009 sales: $20-25 million in revenue
  Total funding: $28 million; last round in March