Naked shorts may have to cover on the name change. They are illegal shorts, and when the company symbol changes, I believe they will be left out in the cold. However, as with all naked shorts, there is no way to know how many there are, or if there are any at all. In the case of RIMM, I have never had a problem shorting it with Ameritrade. They always have short shares, as it is a very heavily traded/shorted stock. They make double commission on same shares when they loan them for shorting, so it's good for them. But I know that Interactive Brokers, the brokerage that most pros use, does not have any shares of RIMM to short, so there may be a shortage @ other brokers too, which encourages naked shorting. Naked shorts may have already covered and gone to legal shorts. That would help to explain the shortage of short shares @ some brokerages, but impossible to know for certain. They may have to cover before end of day today, which should boost the share price a bit. I think it's happening already.
On Monday, all legal shares of RIMM, long or short, will be converted to BBRY. If there is a boost on the name change, I would sell and get out, but I am always biased against RIMM, as I have been shorting it for years.
I will probably short it again on Monday if it pops in the morning.
If you notice, any upward moves are being sold. May be best not to fight the trend, but go with it, at least for now, until the phones are actually released here in U.S. in two months. Then we will see the reaction.