Sender ID:
Sender ID is dynamic (i.e. there are no restrictions on whether it is alpha or numeric) but numeric senders must only have a maximum of 11 characters to ensure delivery.
Content:
There are no additional content restrictions beyond those in our Acceptable Use Policy
Unicode:
Unicode is supported.
Concatenated messages:
Concatenated messages are supported (without delivery receipts).
Other features/restrictions of note:
Delivery Receipts:
Handset delivery receipts are supported except for concatenated messages.
Links:
Global SMS Features Overview (Outbound only)
Global SMS Numbers Features Overview