diff --git a/README.md b/README.md
index bfa05d1..4dc4d9c 100644
--- a/README.md
+++ b/README.md
@@ -77,7 +77,7 @@ npm install -g @textbee/mcp
 
 ### send_sms
 
-Send an SMS to one or more phone numbers or short codes. International format with the country code (for example `+15550100123`) works everywhere. Local numbers and short codes only reach recipients in the sending phone's country. The sending phone is chosen automatically: your default device, otherwise the enabled device with the most recent heartbeat. Optional `device_id`, `sim_subscription_id`, and `scheduled_at`. Returns an `sms_batch_id` for delivery checks when the account uses the SMS queue.
+Send an SMS to one or more phone numbers or short codes. International format with the country code (for example `+15550100123`) works everywhere. Local numbers and short codes only reach recipients in the sending phone's country. The sending phone is chosen automatically: your default device, otherwise the enabled device with the most recent heartbeat. Optional `device_id`, `sim_number`, `sim_subscription_id`, and `scheduled_at`. `sim_number` picks the SIM: `1` for SIM 1, `2` for SIM 2. Omit it and the phone uses its default SIM. If the SIM slot is empty, the message fails and is never sent from another SIM. `sim_subscription_id` is an older option. Android can change it after a SIM swap, so prefer `sim_number`. If both are given, only `sim_number` is used. Returns an `sms_batch_id` for delivery checks when the account uses the SMS queue.
 
 ### get_messages
 
diff --git a/package.json b/package.json
index d9b098e..6cad4cd 100644
--- a/package.json
+++ b/package.json
@@ -42,7 +42,7 @@
   },
   "dependencies": {
     "@modelcontextprotocol/sdk": "1.30.0",
-    "@textbee/sdk": "^0.2.0",
+    "@textbee/sdk": "^0.6.0",
     "zod": "^4.4.3"
   },
   "devDependencies": {
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index e4f21bd..6f4b761 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -12,8 +12,8 @@ importers:
         specifier: 1.30.0
         version: 1.30.0(zod@4.4.3)
       '@textbee/sdk':
-        specifier: ^0.2.0
-        version: 0.2.0
+        specifier: ^0.6.0
+        version: 0.6.0
       zod:
         specifier: ^4.4.3
         version: 4.4.3
@@ -318,8 +318,8 @@ packages:
     cpu: [x64]
     os: [win32]
 
-  '@textbee/sdk@0.2.0':
-    resolution: {integrity: sha512-TVVdIQKW16Iz63vX3ZfVa3RVwOL3vPdIRQznwVBYjtkZwkHoajqM+5KAzpRZP0sEnF1mTlW2RjGsHaBdNeTJOQ==}
+  '@textbee/sdk@0.6.0':
+    resolution: {integrity: sha512-3AX7gJzsmzjZ6+gioNGqnJRDXiVRWZDW7oDAQOoiP//RxkEWRQN83cpEMnxp142L94BQRHsbYJDADeUiGgZjhQ==}
     engines: {node: '>=18'}
 
   '@types/estree@1.0.9':
@@ -1063,7 +1063,7 @@ snapshots:
   '@rollup/rollup-win32-x64-msvc@4.62.4':
     optional: true
 
-  '@textbee/sdk@0.2.0': {}
+  '@textbee/sdk@0.6.0': {}
 
   '@types/estree@1.0.9': {}
 
diff --git a/src/format.ts b/src/format.ts
index 161ddd2..537bd1a 100644
--- a/src/format.ts
+++ b/src/format.ts
@@ -5,7 +5,8 @@ const BODY_PREVIEW_CHARS = 300
 /** Statuses that rarely change. failed and unknown can still change. */
 export const FINAL_STATUSES = ['delivered'] as const
 
-// Local shape until the published SDK types carry issueHistory.
+// Local shapes until the published SDK types carry simSlotIndex and issueHistory.
+type WithSimSlot = { simSlotIndex?: number }
 type WithIssueHistory = { issueHistory?: Array<{ deliveryReport?: boolean }> }
 
 /**
@@ -45,6 +46,10 @@ function formatMessageLine(m: Message, index: number): string {
   const status = m.status ?? 'unknown'
   const header = `[${index}] ${when}  ${direction} ${party}  status=${status}  id=${m._id}`
   const lines = [header, `    ${messageBody(m)}`]
+  const slot = (m as WithSimSlot).simSlotIndex
+  if (typeof slot === 'number') {
+    lines.push(`    Requested SIM ${slot + 1}`)
+  }
   const state = String(m.status ?? '').toLowerCase()
   if (state === 'failed' && (m.errorCode || m.errorMessage)) {
     const code = m.errorCode ?? ''
diff --git a/src/tools.ts b/src/tools.ts
index 5971372..cb51234 100644
--- a/src/tools.ts
+++ b/src/tools.ts
@@ -95,15 +95,23 @@ const sendSmsShape = {
         'textbee choose. Pass it only when the user asks for a specific phone. Ids come ' +
         'from list_devices.',
     ),
+  sim_number: z
+    .number()
+    .int()
+    .min(1)
+    .max(8)
+    .optional()
+    .describe(
+      "Which SIM sends the message: 1 for SIM 1, 2 for SIM 2. Omit to use the phone's default SIM.",
+    ),
   sim_subscription_id: z
     .number()
     .int()
     .min(0)
     .optional()
     .describe(
-      'Which SIM sends on a dual-SIM phone. The server does not validate this: a wrong ' +
-        'value is silently ignored and the phone default SIM is used. The id is shown in ' +
-        'the textbee Android app.',
+      'Older option. The Android id of a SIM. It can change after a SIM swap, and a wrong ' +
+        'value is silently ignored. Prefer sim_number. If both are given, only sim_number is used.',
     ),
   scheduled_at: z
     .string()
@@ -214,6 +222,7 @@ export function buildToolDefinitions(opts: BuildOptions): TextbeeToolDefinition[
       message: string
       recipients: string[]
       device_id?: string
+      sim_number?: number
       sim_subscription_id?: number
       scheduled_at?: string
     }
@@ -261,9 +270,11 @@ export function buildToolDefinitions(opts: BuildOptions): TextbeeToolDefinition[
       message: input.message,
       recipients,
       ...(deviceId !== undefined ? { deviceId } : {}),
-      ...(input.sim_subscription_id !== undefined
-        ? { simSubscriptionId: input.sim_subscription_id }
-        : {}),
+      ...(input.sim_number !== undefined
+        ? { simSlotIndex: input.sim_number - 1 }
+        : input.sim_subscription_id !== undefined
+          ? { simSubscriptionId: input.sim_subscription_id }
+          : {}),
       ...(input.scheduled_at !== undefined ? { scheduledAt: input.scheduled_at } : {}),
     })
 
diff --git a/test/format.test.ts b/test/format.test.ts
index 33b51b3..bb2e577 100644
--- a/test/format.test.ts
+++ b/test/format.test.ts
@@ -48,6 +48,29 @@ describe('formatMessages', () => {
     expect(text).toContain('66b0000000000000000001aa')
   })
 
+  it('shows the requested SIM as a number, one-based', () => {
+    const list: MessageList = {
+      data: [message({ direction: 'sent', status: 'sent', simSlotIndex: 1 } as Partial<Message>)],
+      meta: baseMeta,
+    }
+    const text = formatMessages(list, { direction: 'all', usedCursor: false, order: 'desc' })
+    expect(text).toContain('Requested SIM 2')
+  })
+
+  it('shows SIM 1 for slot 0 and no SIM line when unset', () => {
+    const first: MessageList = {
+      data: [message({ direction: 'sent', status: 'sent', simSlotIndex: 0 } as Partial<Message>)],
+      meta: baseMeta,
+    }
+    const none: MessageList = {
+      data: [message({ direction: 'sent', status: 'sent' })],
+      meta: baseMeta,
+    }
+    const ctx = { direction: 'all', usedCursor: false, order: 'desc' } as const
+    expect(formatMessages(first, ctx)).toContain('Requested SIM 1')
+    expect(formatMessages(none, ctx)).not.toContain('SIM ')
+  })
+
   it('shows the current error on a failed message', () => {
     const list: MessageList = {
       data: [message({ direction: 'sent', status: 'failed', errorCode: 'FCM_SEND_FAILED', errorMessage: 'push failed' })],
diff --git a/test/tools.test.ts b/test/tools.test.ts
index ba3ba8e..c4d6815 100644
--- a/test/tools.test.ts
+++ b/test/tools.test.ts
@@ -170,6 +170,45 @@ describe('send_sms', () => {
     expect(JSON.parse(init.body as string)).not.toHaveProperty('deviceId')
   })
 
+  it('maps sim_number to a zero-based simSlotIndex', async () => {
+    fetchMock.mockResolvedValue(
+      jsonResponse(200, { data: { successCount: 1, failureCount: 0 } }),
+    )
+    await tool('send_sms').handler(
+      { message: 'hi', recipients: ['+15550100123'], sim_number: 2 },
+      {},
+    )
+    const [, init] = fetchMock.mock.calls[0] as [URL, RequestInit]
+    const body = JSON.parse(init.body as string)
+    expect(body.simSlotIndex).toBe(1)
+    expect(body).not.toHaveProperty('simSubscriptionId')
+  })
+
+  it('uses only sim_number when sim_subscription_id is also given', async () => {
+    fetchMock.mockResolvedValue(
+      jsonResponse(200, { data: { successCount: 1, failureCount: 0 } }),
+    )
+    await tool('send_sms').handler(
+      { message: 'hi', recipients: ['+15550100123'], sim_number: 1, sim_subscription_id: 7 },
+      {},
+    )
+    const [, init] = fetchMock.mock.calls[0] as [URL, RequestInit]
+    const body = JSON.parse(init.body as string)
+    expect(body.simSlotIndex).toBe(0)
+    expect(body).not.toHaveProperty('simSubscriptionId')
+  })
+
+  it('sends no SIM fields when none is given', async () => {
+    fetchMock.mockResolvedValue(
+      jsonResponse(200, { data: { successCount: 1, failureCount: 0 } }),
+    )
+    await tool('send_sms').handler({ message: 'hi', recipients: ['+15550100123'] }, {})
+    const [, init] = fetchMock.mock.calls[0] as [URL, RequestInit]
+    const body = JSON.parse(init.body as string)
+    expect(body).not.toHaveProperty('simSlotIndex')
+    expect(body).not.toHaveProperty('simSubscriptionId')
+  })
+
   it('suppresses an identical send inside the dedupe window', async () => {
     fetchMock.mockResolvedValue(
       jsonResponse(200, {