Most parameter (and local variable) names consist of a lowercase prefix followed by one or more words, each beginning with a capital letter. The prefix indicates the parameter type, while the words that follow describe the parameter content. These prefixes are as follows:
| Prefix | Type | Meaning |
| b | BOOL | Boolean (a non-zero specifies TRUE, zero specifies FALSE) |
| ch | char | Character (a one-byte value) |
| dw | DWORD | Long (32-bit) unsigned integer |
| h | 32-bit handle | |
| l | LONG | Long (32-bit) integer |
| lp | Long (32-bit) pointer (also known as Far pointer) | |
| w | WORD | Short (16-bit) unsigned integer |
| s | STR | string |
| sz | ZSTR | ASCII character string that is NULL terminated. |
The Windows Telephony API is "32-bit ready". It uses 32-bit data types almost exclusively to make migration to the 32-bit version of Windows as easy as a recompile. DWORDs are used throughout and handles are 32 bits.