I would not hold my breath waiting for this to happen. I suspect a president can get out of such a thing, although i cannot cite any legal reason why. Considering Barack Obama's distaste for following the rules, it probably would not matter even if their were any lrgal ways to compel his testimony.
Speaking of Obama's distaste for following the rules, here are the six allegations relatig to the subpoena:
1. Obama may have lied about conversations with convicted fraudster Tony Rezko.
2. Obama may have overtly recommended Valerie Jarret for his Senate seat.
3. A supporter of President Obama may have offered quid pro quo on a Jarrett senate appointment.
4. Obama maintained a list of good Senate candidates.
5. Rahm Emanuel allegedly floated Cheryl Jackson's name for the Senate seat.
6. Obama had a secret phone call with Blagojevich.
Some conservatives are already salivating over the prospect of an impeachment. That is a fantasy. the worst that will happen is that Obama will have to explain the discrepancies between past statements and his testimony. We already know he is a liar, so whoop-de-do.