diff --git a/README.md b/README.md
index 4e72e56..edae5e7 100644
--- a/README.md
+++ b/README.md
@@ -106,8 +106,8 @@ smsgate send [options] 'Message content'
 | Option                      | Description                                                                                | Default value | Example                 |
 | --------------------------- | ------------------------------------------------------------------------------------------ | ------------- | ----------------------- |
 | `--id`                      | Message ID, will be generated if not provided                                              | empty         | `zXDYfTmTVf3iMd16zzdBj` |
-| `--phone`, `--phones`, `-p` | Phone number, can be used multiple times or with comma-separated values                    | **required**  | `+19162255887`          |
-| `--sim`                     | SIM card slot number, if empty, the default SIM card will be used                          | empty         | `2`                     |
+| `--phone`, `--phones`, `-p` | Phone number, can be used multiple times or with comma-separated values, E.164 format      | **required**  | `+19162255887`          |
+| `--sim`, `--simNumber`      | One-based SIM card slot number, if empty, the default SIM card will be used                | empty         | `2`                     |
 | `--ttl`                     | Time-to-live (TTL), if empty, the message will not expire<br>Conflicts with `--validUntil` | empty         | `1h30m`                 |
 | `--validUntil`              | Valid until, if empty, the message will not expire<br>Conflicts with `--ttl`               | empty         | `2024-12-31T23:59:59Z`  |
 
diff --git a/internal/commands/messages/send.go b/internal/commands/messages/send.go
index 41db07c..72056d1 100644
--- a/internal/commands/messages/send.go
+++ b/internal/commands/messages/send.go
@@ -25,21 +25,22 @@ var send = &cli.Command{
 		&cli.StringSliceFlag{
 			Name:     "phones",
 			Aliases:  []string{"p", "phone"},
-			Usage:    "Phone numbers",
+			Usage:    "Phone numbers (E.164 format, e.g. +19162255887)",
 			Required: true,
 		},
 		&cli.IntFlag{
-			Name:  "sim",
-			Usage: "SIM card index (1-3)",
+			Name:    "sim",
+			Aliases: []string{"simNumber"},
+			Usage:   "SIM card index (one-based index, e.g. 1)",
 		},
 		&cli.DurationFlag{
 			Name:        "ttl",
-			Usage:       "Time to live",
+			Usage:       "Time to live (duration, e.g. 1h30m)",
 			DefaultText: "unlimited",
 		},
 		&cli.TimestampFlag{
 			Name:     "validUntil",
-			Usage:    "Valid until",
+			Usage:    "Valid until (RFC3339 format, e.g. 2006-01-02T15:04:05Z07:00)",
 			Layout:   time.RFC3339,
 			Timezone: time.Local,
 		},