Curt,
As I mentioned in another thread, the interest rate on the underlying loans in a MBS is typically around 0.5% higher than the pass-through coupon rate.
This 1/2% difference is the servicing and guaranty premium. The guaranty premium charged by Ginnie Mae on a Ginnie I pool is .06% leaving the lender with a servicing premium of 0.44%. So on a principal of $100,000 the lender is paid $440/year to service the loan. The present value of this stream of income is worth about 2% to 2.5%, in the same manner as the yield premium for a rate 3/8 to a 1/2 over par is worth 2% to 2.5%.
Here is a link to the Ginnie Handbook for servicers if you would like more information on guaranty and servicing fees: http://www.ginniemae.gov/guide/guidtoc.asp?Section=Issuers#chap
On Friday a popular wholesale lender was offering 100.25 (0.25 premium) on an FHA 30 year at 5.00%. One large correspondent lender was paying 102.5 on that same loan. The equivalent MBS is the 4.5 coupon. On Friday the Feb GN coupon was about 102.50. As has been discussed there is a large variation in price between lenders coming in and out of the market to regulate their pipeline and the amount of loans flowing into operations.
So how much income does that represent? The wholesale lender in this example was making about 4.5%. 2.25 (value of the servicing premium) + 2.5 (premium on 4.5 coupon) - .25 (YSP pd to originator) = 4.5%.
The correspondent income was 2.25 (value of the servicing premium) + 2.5% (premium on 4.5 coupon) - 2.5% (paid to originator) = 2.25% income.
A national retail lender was quoting retail customers 5.00% with 1.00% origination on an FHA 30 yr. Their gross income on that loan would be about 2.25% SRP + 2.5% coupon premium + 1.0% origination = 5.75% in gross income.