Problem
The bond information in the below table as of last close on Nov. 9, 2022 (all yields are expressed in annual term):
Select Apple Inc. vs. The Boeing Company Bonds:
| Symbol | Callable | Coupon | Maturity | Moody's | S&P | Price | Yield | 
| AAPL4984115 | Yes | 0.750% | 05/11/2023 | Aaa | AA+ | 98.228 | 4.432% | 
| AAPL4984119 | Yes | 1.125% | 05/11/2025 | Aaa | AA+ | 91.575 | 4.750% | 
| AAPL4984120 | Yes | 1.650% | 05/11/2030 | Aaa | AA+ | 79.968 | 4.874% | 
| AAPL4984116 | Yes | 2.650% | 05/11/2050 | Aaa | AA+ | 62.413 | 5.248% | 
| BA4983333 | Yes | 4.508% | 05/01/2023 | Baa2 | BBB- | 99.720 | 5.118% | 
| BA4983334 | Yes | 4.875% | 05/01/2025 | Baa2 | BBB- | 97.928 | 5.788% | 
| BA4983328 | Yes | 5.150% | 05/01/2030 | Baa2 | BBB- | 93.329 | 6.283% | 
| BA4983330 | Yes | 5.805% | 05/01/2050 | Baa2 | BBB- | 86.404 | 6.917% | 
Explain the observed differences in yield. In general, what are callable bonds? What are the differences between investment grade bonds vs. high yield bonds?